United Nations experts are investigating the alleged use of chemical weapons in Syria as the United States prepares for the possibility of a punitive strike against President Bashar Assad's regime, blamed by the Syrian opposition for the attack. The international aid group Doctors Without Borders says at least 355 people were killed in the Aug. 21 attack in a suburb of Damascus, the Syrian capital. Here's a look at key Syria developments around the world Friday amid heightened tensions over potential military action: French President Francois Hollande said his country can go ahead with plans to strike Syria for allegedly using chemical weapons despite the British parliament's failure to endorse military action. He told the newspaper Le Monde that the "chemical massacre of Damascus cannot and must not remain unpunished." U.N. experts were on their last day of an investigation into the attack. After an early morning delay, three U.N. vehicles left a Damascus hotel for more on-site visits. It was not immediately known where they went. Shops and supermarkets in Damascus were filled with people stocking up on bread, canned food and other necessities ahead of expected strikes, but there were no apparent signs of panic or shortages. President Barack Obama convened senior national security advisers at the White House to discuss plans for possible military action against Syria. After the meeting, a public release was expected of a report on intelligence the U.S. has gathered about the chemical weapons attack. U.S. Defense Secretary Chuck Hagel said the Obama administration was consulting with allies to "further develop the facts" about last week's alleged chemical weapons attack, and options for a response. U.N. Secretary-General Ban Ki-moon will meet privately with the ambassadors of the five permanent Security Council members as part of his efforts to urge the divided council to come together and act on Syria's crisis. Ban returned to New York Thursday evening after cutting short a trip to Europe to be ready to receive a briefing from the chemical weapons inspectors. Presidential foreign policy adviser Yuri Ushakov expressed puzzlement over why the U.N. team was leaving "when there are many questions about a possible use of chemical weapons in other areas in Syria." He said Russia has not seen the U.S. intelligence that Washington claims proves the role of the Syrian government in last week's alleged chemical weapons attack. Treasury chief George Osborne warned that Britain should not turn its back on the world after the stunning parliamentary defeat of a government motion for military intervention in Syria. He told the BBC there will be "national soul-searching" about Britain's global role after the "no" vote. German government spokesman Steffen Seibert said Germany isn't considering joining military action against Syria and hasn't been asked by others to do so. Berlin has called for the international community to take a "clear position" following the alleged chemical attack, but has left open what exactly that might entail. Followers of anti-American Shiite cleric Muqtada al-Sadr held rallies in Baghdad and the southern Iraqi city of Basra to denounce any Western strikes against Syria. In the capital, about 2,000 Sadrists demonstrated while chanting anti-American slogans after Friday prayers. About 3,000 Sadrists rallied in Basra, some carrying banners reading "No to America."