"They are late. They came six days late," said al-Ahmad, referring to the time it took the U.N. team to arrive. "All the people have already been buried," he added via Skype, after returning from the hospital where he witnessed the U.N. visit.
The sounds of explosions could be heard in the background. Al-Ahmad said heavy shelling resumed as soon as the U.N. experts left the area following a lull.
In videos uploaded by the Moadamiyeh media office, U.N. inspectors in blue helmets and body armor were seen interviewing hospital patients.
"After the shells landed, I went downstairs and ... felt dizzy. I fell down, nauseous. Everything became distorted," one bearded man was seen telling the U.N. official.
One video showed a man lying on a stretcher in the presence of U.N. experts and doctors in the room, his legs twitching uncontrollably. In another, a U.N. expert was seen conducting tests on a missile.
The U.S., France, Britain and Israel said a military response against the Syrian regime should be an option. Germany suggested 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," according to Steffen Seibert, a spokesman for Chancellor Angela Merkel.
U.S. Defense Secretary Chuck Hagel, speaking to reporters after meeting with his Indonesian counterpart, said the Obama administration "is considering all different options," and that "if there is any action taken, it will be in concert with the international community and within the framework of a legal justification."
French Foreign Minister Laurent Fabius said "all the options are open. The only option that I can't imagine would be to do nothing."
Russia said Western nations calling for military action have no proof the Syrian government was behind any chemical attacks.
Syrian activists and opposition leaders have said that between 322 and 1,300 people were killed in the alleged chemical attack.
Russian Foreign Minister Sergey Lavrov said the countries calling for military action have assumed the role of "both investigators and the U.N. Security Council" in probing the incident.
Lavrov likened the situation in Syria to the period before the U.S.-led invasion of Iraq in 2003. He said "the use of force without a sanction of the U.N. Security Council is a crude violation of the international law."
Assad told the Russian newspaper Izvestia that accusations his troops used chemicals were "politically motivated."
"This is nonsense," Assad was quoted as saying. "First they level the accusations, and only then they start collecting evidence."
Assad said attacking such an area with chemical weapons would not make sense for the government, because there was no clear front line between regime and rebel forces.
"How can the government use chemical weapons, or any other weapons of mass destruction, in an area where its troops are situated?" he asked.
Commenting on a possible strike by the U.S., Assad said: "They can start a war but they will not know where it will spread or how it will end. Superpowers can launch wars but they cannot win them."
Asked what the U.S. would face in any intervention, Assad answered: "What it suffered in all its wars from Vietnam until now: Failure."
Karam reported from Beirut. Associated Press writers Albert Aji in Damascus, Bassem Mroue in Beirut, Nataliya Vasilyeva in Moscow, Matthew Lee and Julie Pace in Washington, John Heilprin in Geneva, Robert Reid in Berlin, and Peter Spielmann in New York contributed to this report.