U.N. Secretary-General Ban Ki-moon is urging world powers to hold off on possible military action against Syria until a U.N chemical weapons inspection team completes its work in the country.
Mr. Ban said Thursday that the team will leave the country by Saturday and report its findings to him.
He said "diplomacy should be given a chance" as the U.S. and other Western powers consider their response to the Syrian government's alleged use of chemical weapons against civilians last week.
The U.N. team left Damascus in a convoy on Thursday to begin its third day of inspections.
British Prime Minister David Cameron is meeting with parliament on Thursday to discuss the Syria situation.
Amid mounting pressure from lawmakers, his government said Wednesday that Britain would not take part in any military action against Syria until the U.N. team had a chance to report its findings.
In Washington, White House officials plan to brief members of Congress, on Thursday, about intelligence on the alleged poison gas attacks that killed hundreds of civilians in Damascus suburbs.
The Syrian government denies having any role in the alleged attacks. And state media reports say Syrian President Bashar al-Assad said Thursday his country would defend itself against any aggression and emerge "victorious."
Iran warned any Western action against Syria would result in the "imminent destruction of Israel," a U.S. ally in the region.
US Appeals to New Iranian President for Release of 3 Americans
The United States has issued an appeal to Iran's new president, asking for his help in returning three Americans to their families after lengthy detentions in the Islamic Republic.
The State Department, in a statement Wednesday, said Washington is "respectfully" asking President Hasan Rouhani to facilitate the return of 65-year-old Robert Levinson, and dual American-Iranian citizens Amir Hekmati and Saeed Abedini.
Levinson, a retired FBI agent and father of seven children, went missing from Kish Island, Iran in March 2007 while researching a smuggling case as a private investigator. The U.S. statement said Abedini is serving an eight-year prison term on charges related to his religious beliefs, while Hekmati -- a former U.S. Marine -- is being held on what U.S. officials call "false espionage charges."
The U.S. statement noted that President Rouhani, who took office earlier this month, has publicly voiced hope for improved relations with the global community.