U.S. Secretary of State Antony Blinken was meeting the leaders of Turkiye and Greece on Saturday at the start of a week-long trip aimed at calming tensions that have spiked across the Middle East since Israel's war with Hamas began in October.

The Biden administration's most senior diplomat began in Istanbul, meeting Turkiye's President Tayyip Erdogan, a strong critic of Israel's military actions in Gaza.

In the talks, Blinken "emphasized the need to prevent the conflict from spreading, secure the release of hostages, expand humanitarian assistance and reduce civilian casualties," State Department spokesperson Matthew Miller said.

Blinken also stressed the need to work toward broader, lasting regional peace that ensures Israel's security and advances the establishment of a Palestinian state, he said.

Blinken and Foreign Minister Hakan Fidan had earlier discussed the war and humanitarian crisis in Gaza, plus Turkiye's process to ratify Sweden's membership of the NATO military alliance, Turkiye's foreign ministry said in a statement.

U.S. officials have been frustrated by the lengthy process, but are confident Ankara will soon approve Sweden's accession after it won the Turkish parliament's backing last month, said a senior State Department official traveling with Blinken, speaking on condition of anonymity.

U.S. lawmakers have held up the sale of F-16 fighter jets to Turkiye until it signs off on the addition of Sweden to the North Atlantic Treaty Organization.

Sweden, which along with Finland applied to join NATO following Russia's invasion of Ukraine in early 2022, would become the alliance's 32nd member. Finland joined last year.

BLINKEN TO VISIT GREECE

Blinken will later travel to the island of Crete to meet Greek Prime Minister Kyriakos Mitsotakis. Fellow NATO member Greece is awaiting approval by the U.S. Congress of a sale of F-35 fighter jets.

"We'll be discussing this issue. I think there will be positive developments," Greek Foreign Minister George Gerapetritis told Greek Skai television.

Blinken's tour will include Arab states, Israel and the occupied West Bank, where he will deliver a message that Washington does not want a regional escalation of the Gaza conflict.

The U.S. official said Turkiye has relationships with many parties in the conflict, a reference to its ties to U.S. adversary Iran and Palestinian militant group Hamas. Unlike the U.S., Turkiye does not view Hamas as a terrorist group and hosts some of its members.

The war began when Hamas fighters attacked Israel on Oct. 7, killing 1,200 people and taking 240 hostages.

Israel's retaliatory offensive has killed 22,700 Palestinians, according to Palestinian officials, and the conflict has spilled into the West Bank, Lebanon and Red Sea shipping lanes.

Blinken also hopes to make progress in talks on how Gaza could be governed if and when Israel achieves its aim of eradicating Hamas.

Washington wants regional countries, including Turkiye, to play a role in reconstruction, governance and potentially security in the Gaza Strip, which has been run by Hamas since 2007, the official said.