U.S. President Barack Obama said he has not decided how the U.S. would respond to the Aug. 21 attacks near Damascus that, according to the group Doctors Without Borders, killed 355 people.
However, Obama signaled Wednesday that the U.S. is moving toward a punitive strike, saying he has "concluded" that Assad's regime is behind the attacks and that there "need to be international consequences."
Both Obama and British Prime Minister David Cameron were trying to shore up domestic political support Thursday for possible military action.
The Obama administration was planning a teleconference briefing Thursday on Syria for leaders of the House and Senate and national security committees, U.S. officials and congressional aides said.
Cameron convened Parliament for an emergency meeting to vote on possible international action against Syria. Cameron promised he would not go to war until the U.N. weapons team has had a chance to report its findings.
In Vienna, U.N. Secretary-General Ban Ki-moon said Thursday he spoke to Obama a day earlier about ways of expediting the U.N. investigation.
Ban said the U.N. team is to leave Syria on Saturday, and suggested that the Western powers hold off on any decisions until the inspectors have presented their findings.
Ban said he told Obama the U.N. investigators "should be allowed to continue their work as mandated by the member states and I told him that we will surely share our information and our analysis."
"Diplomacy should be given a chance, and peace given a chance," Ban said. "It's important that all the differences of opinions should be resolved through peaceful means and through dialogue."
On Thursday, the U.N. inspectors left the Four Seasons Hotel in Damascus in a convoy of six vehicles.
Their destination was not immediately known, although several anti-regime activists, contacted by Skype, said they were told by residents that the inspectors were touring the suburb of Zamalka east of Damascus.
The U.N. team did not issue a statement about its plans Thursday.
On two previous tours this week, the inspectors visited a western suburb of the city as well as Zamalka. They took biological samples from suspected victims. Ban has said the samples would be analyzed and presented to the U.N. Security Council.
Prospects of a Western military strike and possible Syrian regime retaliation have sparked growing anxiety among civilians in Syria and neighboring countries.
In Damascus, some residents have begun stocking up on bottled water and canned food. Israelis have been standing in long lines to get government-issue gas masks. And the stream of Syrian refugees heading to Lebanon has picked up considerably in recent days.
Israeli police spokesman Micky Rosenfeld said officers were deployed to maintain order in the northern city of Haifa, where more than 5,000 people jostled in line as they waited for their protective kits. A sports arena there was being used as a distribution center to accommodate the crowds.
Israel's postal service, which oversees the distribution, said an angry mob forcibly took gas masks from a distribution center in Jerusalem on Wednesday, leading to the site's indefinite closure.
Israel has also called up reservists and deployed missile defense batteries in preparation for a possible Syrian response to an American attack.
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