WASHINGTON -- U.S. President Donald Trump confirmed Friday he is under federal investigation and appeared to single out a senior Justice Department official for criticism, firing off tweets underscoring his growing frustration with the persistent focus on Russia's involvement in the 2016 election and possibly his campaign.

the president wrote.

The morning missive appeared to refer to Rod Rosenstein, the deputy attorney general. Last month, Rosenstein sent a memo to Trump raising concerns over FBI Director James Comey -- concerns the White House then cited as a central reason for Comey's firing.

Days after Comey was abruptly ousted, Rosenstein appointed Robert Mueller as special counsel to investigate Russian involvement in the 2016 presidential election and possible collusion with the Trump campaign. Mueller also has expansive powers to investigate any matters that develop from his initial investigation.

It was unclear whether the president's comment confirming he was under investigation was based on direct knowledge or media reports that Mueller is examining whether the president obstructed justice by firing Comey. Still, the snowballing investigation has deeply angered Trump, who denies he has any nefarious ties to Russia. He's increasingly focused his anger at both Rosenstein and Mueller, according to advisers and confidants, viewing the two as part of a biased effort to undermine his presidency.

Sen. Dianne Feinstein, the top Democrat on the Senate Judiciary Committee, said she was that Trump will fire both Mueller and Rosenstein.

"The message the president is sending through his tweets is that he believes the rule of law doesn't apply to him and that anyone who thinks otherwise will be fired," Feinstein said. "That's undemocratic on its face and a blatant violation of the president's oath of office."

Rosenstein has been overseeing the Russia probe since Attorney General Jeff Sessions recused himself. But Rosenstein, too, may ultimately have to hand off oversight of the probe given his own role in Comey's firing.

Earlier this month, Rosenstein told The Associated Press that "if anything that I did winds up being relevant to his investigation then, as Director Mueller and I discussed, if there's a need from me to recuse, I will."

Trump's tweets come after the top lawyer for his transition team warned the organization's officials to preserve all records and other materials related to the Russia probe. An official of Trump's transition confirmed the lawyer's internal order, which was sent Thursday.

The transition official spoke on condition of anonymity because the person was not authorized to discuss post-election decisions publicly.

The order by the general counsel for the transition team casts a wide net on documents that could shed light on ties between Trump's presidential campaign and representatives of Russia's government. The order also covers separate inquiries into several key Trump associates including former National Security Adviser Michael Flynn, campaign adviser Paul Manafort, foreign policy aide Carter Page and outside adviser Roger Stone.

The White House has directed questions for details to outside legal counsel, which has not responded.

Vice-President Mike Pence has also hired a private lawyer to represent his interests in the expanding probe. Pence headed the Trump transition until Inauguration Day.

The transition official said the organization has also separately asked the General Services Administration to preserve records from the Trump transition that were transferred to its facilities after the inauguration. The transition, a non-profit structurally separate from the Trump campaign, continues to operate with a small staff.

The memo sent Thursday asks for records related to foreign travel, contacts with Russian "officials, agents or nationals" and background investigations into the top Trump associates now targeted by Mueller's probe. The memo asks for preservation of electronic communications and data, telephone logs, audio recordings, videos, calendars and other items.

Friday's tweets are the latest in a week of angry social media responses by the president after a report by The Washington Post that Mueller was looking into whether Trump obstructed justice.

he asked at one point.

Trump wrote in his first tweet.

Associated Press writers Stephen Braun and Mary Clare Jalonick contributed to this report.

WASHINGTON - The latest on the ongoing investigations into allegations of Russia interference in the 2016 U.S. election (all times local):

12:25 p.m.

The top Democrat on the Senate Judiciary Committee says she is "increasingly concerned" that President Donald Trump will attempt to fire Special Counsel Robert Mueller and Deputy Attorney General Rod Rosenstein.

Mueller is investigating Russian interference in U.S. elections and possible Russian ties to the Trump campaign. Trump confirmed in a tweet Friday he was under investigation and appeared to take aim at Rosenstein, calling the investigation a "witch hunt."

California Sen. Dianne Feinstein said Trump's tweets are sending a message "that he believes the rule of law doesn't apply to him and that anyone who thinks otherwise will be fired."

She said Trump has "embarked on an effort to undermine anyone with the ability to bring any misdeeds to light" and the Senate shouldn't let that happen.

Feinstein also is a member of the Senate Intelligence committee, which is conducting its own Russia probe.

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11:15 a.m.

The Senate Intelligence Committee is holding a public hearing next week to gather more information on Russia's interference in last year's elections.

Wednesday's session will focus on Russia's efforts to hack into state election systems, potential threats in upcoming election cycles, and whether states are well positioned to respond to those threats.

The panel is conducting both open hearings and closed sessions as it investigates Russian efforts to influence last year's campaign. The intelligence committee is the lead congressional panel on the Russia hacking scandal, including highly publicized hearings with fired FBI Director James Comey and Attorney General Jeff Sessions.

Next week's witnesses include officials from the FBI and the Department of Homeland Security, election officials, and an expert on election security.

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9:49 a.m.

The top lawyer for the Trump transition team has ordered the organization's staff to preserve all records and other materials related to the widening investigation by special counsel Robert Mueller into contacts between the Trump campaign and Russian representatives.

The move ordered Thursday by the transition's general counsel cast a wide net on documents tied to the Russia investigation as well as inquiries into the activities of Trump associates. Those associates include former national security adviser Michael Flynn, campaign chairman Paul Manafort, foreign policy aide Carter Page and outside adviser Roger Stone.

The move was confirmed by a transition official who spoke on condition of anonymity to discuss post-election decisions.

The order came the same day that Vice-President Mike Pence hired an outside lawyer to represent his legal interests.

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9:20 a.m.

U.S. President Donald Trump says he is being investigated for firing FBI Director James Comey by the man who told him to do it.

In his latest tweet, the president seemed to confirm he is under investigation for possible obstruction of justice. It wasn't clear whether he was basing his tweet on direct knowledge or on media reports.

The president wrote, ""

Trump may be referring to Deputy Attorney General Rod Rosenstein, who in a memo to Trump raised concerns over Comey's performance. But Robert Mueller has been appointed special counsel to investigate Russian involvement in the 2016 presidential election and possible collusion with the Trump campaign.

There has been no indication that Mueller told Trump to fire Comey.

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9:10 a.m.

President Donald Trump says the economy is improving and job numbers are up, despite the "phoney Witch Hunt" against him.

The president tweeted Friday, ""

U.S. employers pulled back on hiring in May by adding only 138,000 jobs, though the gains were enough to help nudge the unemployment rate down to a 16 year-low.

The Labor Department this month that the jobless rate fell to 4.3 per cent the lowest level since 2001, from 4.4 per cent. Still, the rate declined mainly for a less-than-encouraging reason: People stopped looking for work in May and so were no longer counted as unemployed.

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8:40 a.m.

President Donald Trump is touting his social media following, saying he can deliver his message directly to voters instead of going through the "fake news media."

The president tweeted Friday, ""

Trump is an avid user of Twitter, with over 32 million followers on his personal account and more than 18 million people on the official presidential account. He also has millions of followers on his official Facebook pages.

Not all of Trump's social media followers are supporters. And Democrats and Republicans alike have criticized his use of Twitter, particularly amid the ongoing investigation into Russia's interference in the 2016 presidential election.

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8:05 a.m.

President Donald Trump says it's "sad" that seven months of investigations and hearings into possible links between his campaign and Russia have been fruitless.

The president tweeted Friday, ""

His comments follow revelations that special counsel Robert Mueller is examining whether Trump obstructed justice by firing FBI Director James Comey. Mueller is now leading the investigation into whether Russia interfered in the 2016 presidential election.

Trump has called a "phoney story" and a "WITCH HUNT." He has questioned why investigators don't dig into the links between the Democrats and the Russian government, including his general election opponent, Hillary Clinton.