Secretary of State John Kerry says chemical weapons were used in Syria, accuses President Bashar Assad of destroying evidence, and says the U.S. has additional information about the attack and will soon make it public. Kerry calls the attack a "moral obscenity" that should shock the conscience of the world.
President Francois Hollande says time is running out for the Syrian regime and airstrikes are a possibility.
"Everything will come into play this week," he told Le Parisien newspaper. "There are several options on the table, ranging from strengthening international sanctions to airstrikes to arming the rebels.
Hollande spoke with President Barack Obama on Sunday and told him France, like Britain, would support him in a targeted military intervention, according to the paper.
"It's still too early to say categorically what will happen," he was quoted as saying. "The U.N. experts are going to investigate on site. We also have to allow time for the diplomatic process. But not too much. We can't go without a reaction when confronted with chemical weapons."
Foreign Minister Laurent Fabius said "all the options are open. The only option that I can't imagine would be to do nothing."
Germany suggests for the first time it may support the use of force if a chemical weapons attack is confirmed.
"The suspected large-scale use of poison gas breaks a taboo even in this Syrian conflict that has been so full of cruelty," Chancellor Angela Merkel's spokesman, Steffen Seibert, said. "It's a serious breach of the international Chemical Weapons Convention, which categorically bans the use of these weapons. It must be punished, it cannot remain without consequences."
Germany has "very clear evidence that this was a chemical weapons attack," Seibert said. He declined to speculate on what kind of response might now be needed in Syria, but repeatedly refused to rule out the use of force.
Foreign Minister Sergei Lavrov says Western nations calling for military action against Syria have no proof the regime is behind the alleged attack.
Lavrov said the countries calling for action have assumed the role of "both investigators and the U.N. Security Council" in probing the incident.
"They cannot produce evidence, but keep on saying that the 'red line' has been crossed and they cannot wait any longer," he said at a Moscow news conference.
Lavrov likened the situation in Syria to the run-up before the 2003 Iraq invasion. He warned against military intervention in Syria, saying "the use of force without a sanction of the U.N. Security Council is a crude violation of international law."
Foreign Secretary William Hague says disagreements among the five U.N. Security Council members have prevented any action over Syria from being taken for too long and "complete unity" wasn't necessary to launch a response.
"We cannot in the 21st century allow the idea that chemical weapons can be used with impunity," he said.
British Prime Minister David Cameron's office said lawmakers could be recalled to debate any potential action over Syria as soon as this week and that Cameron plans to meet with national security advisers Wednesday. Cameron's spokesman said London reserves "the ability to take action swiftly if needed."
Cameron later called Vladimir Putin and told the Russian leader there was little doubt that Syrian forces had been responsible and prevented immediate U.N. access to the site, "suggesting they had something to hide," the premier's office said. Both agreed that any use of chemical weapons would merit a serious response from the international community, but Putin said there was no evidence about whether they had been used in Syria and, if so, who was responsible.
Foreign Minister Ahmet Davutoglu says his country would take part in an international coalition against Syrian President Bashar Assad's regime if the U.N. failed to come up with sanctions to punish Syria for the alleged use of chemical weapons.
Turkey was once a close Syrian ally, but turned into one of Assad's harshest critics and is a key supporter of Syrian rebels. Turkey has repeatedly struck back at Syrian territory in response to shelling, mortar rounds or fire from across the border since shells from Syria struck a Turkish village in October, killing five people.
Speaking to reporters in Seoul, South Korea, U.N. Secretary-General Ban Ki-moon says "if proven, any use of chemical weapons by anyone under any circumstances is a serious violation of international law and an outrageous crime. We cannot allow impunity in what appears to be a grave crime against humanity."
In New York, U.N. spokesman Farhan Haq said: "Despite the passage of a number of days, the secretary-general is confident that the team will be able to obtain and analyze evidence relevant for its investigation of the Aug. 21 incident."
EU foreign policy chief Catherine Ashton says a decision about military intervention in Syria hasn't been made yet and the support of the U.N. Security Council for any such action remains "extremely important."
Ashton told reporters in Estonia's capital, Tallinn, the world "needs to find a political solution" for Syria's bloodshed. She said it is difficult for the 28-member EU to reach a joint conclusion, but the bloc is considering "various options."
Ashton said she has stressed the need to end the violence in "recent conversations with China and Russia." She also said it is important that U.N. weapons inspectors are allowed to examine the evidence of a possible chemical weapons attack "as quickly as possible to reach a conclusion."
President Shimon Peres calls on the U.N. to appoint the Arab League to set up a temporary government in Syria to stop the bloodshed.
Peres' comments marked the highest-profile Israeli call for international intervention in neighboring Syria. Israel has been careful to stay on the sidelines of Syria's civil war, which has killed more than 100,000. But international demands have been growing for action amid the chemical weapons attack allegations.
Peres said "foreigners will not understand what is going on in Syria" so the U.N. should task the Arab League with setting up a government.