The United States is considering launching a punitive strike against the regime of Syrian President Bashar Assad, blamed by the U.S. and the Syrian opposition for an Aug. 21 alleged chemical weapons attack in a rebel-held suburb of the Syrian capital of Damascus. The U.S. said the attack killed 1,429 people, including at least 426 children. Those numbers are significantly higher than the death toll of 355 provided by the aid group Doctors Without Borders.

President Barack Obama said he has decided that the United States should take military action against Syria but will seek congressional authorization for the use of force.

Here's a look at key Syria developments around the world Sunday amid heightened tensions over potential military action:

UNITED STATES:

Secretary of State John Kerry asserted the United States has evidence of sarin gas use in Syria. A day after President Barack Obama stepped back from his threat to launch an attack, Kerry says in interviews that the administration learned of the sarin use through samples of hair and blood provided to Washington by first responders in Damascus.

SYRIA:

A Syrian state-run newspaper said Obama's decision to seek congressional approval before taking military action against Syria marks "the start of the historic American retreat." The Al-Thawra daily said in a front-page editorial that Obama's reluctance to carry out strikes stems from his "sense of implicit defeat and the disappearance of his allies."

UNITED NATIONS:

Secretary-General Ban Ki-Moon was expected to be briefed by the head of the UN chemical weapons inspection team, Ake Sellstrom. The team collected samples from alleged chemical weapons attack sites in Syria that are expected to be repackaged in the Netherlands and sent to laboratories around Europe to check them for traces of poison gas. Evidence would have to be analyzed in the laboratories before any report is made to member states.

FRANCE:

Francois Fillon, France's ex-prime minister and leading figure in the opposition UMP party, said the French parliament should get the same privilege the U.S. Congress will have to vote on Syria intervention. France's parliament is scheduled to debate the issue Wednesday, but no vote is scheduled. President Francois Hollande backs Obama's decision for a strike. The French constitution doesn't require such a vote unless and until a French military intervention lasts longer than four months.

VATICAN:

Pope Francis condemned the use of chemical weapons and called for a negotiated settlement to the civil war in Syria. Francis spoke with anguish about Syria: "My heart is deeply wounded by what is happening in Syria and anguished by the dramatic developments" on the horizon, an apparent reference to the U.S. and France considering a military strike against the Syrian regime.

MEDITERRANEAN SEA:

Five U.S. Navy destroyers were in the eastern Mediterranean Sea -- armed with dozens of Tomahawk cruise missiles, which have a range of about 1,000 nautical miles (1,852 kilometres) and are used for precise targeting. Obama announced Friday that "we are prepared to strike whenever we choose."

IRAN:

Iranian state TV said an Iranian parliamentary delegation in Damascus visited with Syrians allegedly injured in chemical weapons attacks that the Assad regime blames on rebels. They were also expected to meet with the Syrian prime minister and foreign minister.

ISRAEL:

Israeli Prime Minister Benjamin Netanyahu Israel's prime minister tried to soothe a jittery nation unnerved by the standoff between the U.S. and Syria, saying Israel is "calm and self-assured" and ready for "any possible scenario." More Israelis lined up to receive free gas masks, fearing Israel could be targeted in retribution if Syria is hit by a punitive strike.

TURKEY:

Syrian refugees continued crossing the border into Turkey, despite the delay of a possible U.S. military strike targeting Assad's government. Refugee Mohammed Yaser said arms shipments to rebels would hurt Assad more than a U.S. strike: "If they give us weapons, we can deal with it in one week."