Here's a look at key Syria developments around the world Thursday amid heightened tensions over potential military action:
Leaders at the forefront of the geopolitical standoff over Syria's civil war gathered in St. Petersburg and started the two-day meeting of the Group of 20 leading world economies, with the threat of missiles over the Mediterranean eclipsing economic issues that usually dominate the annual summit. Differences over Syria have heightened tensions between Obama and Russian President Vladimir Putin since the civil war in Syria started in 2011.
Putin's spokesman, Dmitry Peskov, said the U.S. should wait for the U.N. inspectors' report on their investigation into chemical attack before intervening militarily, adding that Washington's evidence of Syrian regime involvement isn't strong enough. He insisted the U.N. Security Council is the only body that can authorize use of force. The Kremlin's chief of staff said Russia has been sending warships to the Mediterranean Sea for possible evacuation of Russian citizens from Syria. Sergei Ivanov told Russian news agencies the country boosted its naval presence "primarily" to organize a possible evacuation.
Prime Minister David Cameron said British scientists have found new evidence that poison gas was used last month outside the Syrian capital. Cameron told BBC television the evidence being examined at England's Porton Down Laboratory "further shows the use of chemical weapons in that Damascus suburb."
Syrian government troops battled al-Qaida-linked rebels for a second day over the regime-held Christian village of Maaloula in western Syria. Rami Abdul-Rahman, the director of the Britain-based Observatory for Human Rights, said the fighters included members of the of al-Qaida affiliated Jabhat al-Nusra group.
Obama pressed skeptical lawmakers in phone calls from St. Petersburg to give him the authority to use U.S. military force against Syria while the administration. Obama's advisers were lobbying Congress in closed-door meetings for military strike authorization.
U.S. Ambassador Samantha Power lashed into Russia at the United Nations, accusing Moscow of holding the Security Council "hostage" by blocking action against Syria. In St. Petersburg, U.N. Secretary-General Ban Ki-moon said the situation in Syria has "no military solution. There is only a political solution which can bring peace and end this bloodshed right now."
European Union President Herman Van Rompuy urged U.N. investigators to release information as soon as possible about a chemical weapons attack in Syria so the international community can decide how to respond. Rompuy said in St. Petersburg that the attack "was a blatant violation of international law and a crime against humanity." He said it is too early for a military response,
Russian Foreign Ministry spokesman, Alexander Lukashevich, warned that a U.S. strike on Syria's atomic facilities might result in a nuclear catastrophe and urged the U.N.'s nuclear agency to conduct a risk analysis. Gill Tudor, spokeswoman for the Vienna-based International Atomic Energy Agency, said the IAEA is ready to "consider the questions raised" by Lukashevich if it receives a formal request from Moscow.
German Chancellor Angela Merkel said she doubts world leaders can agree on what to do about Syria's civil war despite frenzied diplomatic efforts because of disagreement over who was responsible for the gas attack. She said: "I do not believe yet that we will reach a joint position."
Pope Francis urged world leaders to abandon the "futile pursuit" of a military solution in Syria and work for dialogue and negotiation to end the conflict. In a letter to Putin, the pope lamented that "one-sided interests" had prevailed in Syria. He said those interests allowed the "senseless massacre" of innocent people.
Italy's culture ministry decided it's not the right time to send a Botticelli masterpiece on loan to Israel with tensions high over Syria. The ministry said it decided against transporting the 15th-century "The Annunciation of San Martino alla Scala" from the Uffizi Gallery in Florence to the Israel Museum in Jerusalem, where it to go on display for several months starting Sept. 17.
China warned of global economic risks linked to a potential U.S.-led military intervention in Syria's civil war. Chinese Vice Finance Minister Zhu Guangyao says such "military action would definitely have a negative impact on the global economy, especially on the oil price."