Moallem blamed rebel forces for failing to guarantee the U.N. group's safety and denying that its forces have delayed inspections by continually shelling Ghouta.
Video posted Tuesday to YouTube purported to show the area being shelled, though CNN could not verify this video's authenticity.
Yet Biden reiterated the claim that Syrian forces were shelling the suspected chemical attack site. And U.S. State Department spokeswoman Marie Harf said it may be too late for a valid inspection of what happened -- saying "too much time has passed" and accusing al-Assad's government of using the U.N. investigation "as a stalling tactic or a charade to hide behind."
The United States, meanwhile, is conducting its own investigation: An intelligence report detailing evidence of the alleged attack could be released as early as Tuesday, a U.S. official told CNN. The report will include forensic evidence and intercepted communications among Syrian military commanders, according to the official.
The vice president said that beyond whatever inspectors do or do not find, common sense and the recent past point to one culprit.
"The Syrian regime are the only ones who have the weapons, have used chemical weapons multiple times in the past, have the means of delivering those weapons, have been determined to wipe out exactly the places that were attacked by chemical weapons," he said Tuesday.
Russia leads international charge against strikes
The calls for a military response were not without opposition.
Russia is leading the charge internationally, with Foreign Minister Sergey Lavrov having said there is no proof yet Syria's government is behind last week's chemical attack. His office compares the Western allegations against Syria to claims Iraq was hoarding weapons of mass destruction before the U.S. invasion in 2003 -- allegations that fell apart once American troops began searching for them.
And Tuesday, Russia's foreign ministry accused Washington of trying to "create artificial groundless excuses for military intervention."
Moscow bemoaned the U.S. postponement of a meeting that was scheduled for Wednesday in The Hague, where top diplomats from both countries had planned to discuss the war in Syria.
And Russia criticized the United States for, in its view, trying to bypass the U.N. Security Council to take action on the reported chemical attack.
Should anything be moved through the U.N. council, Russia -- which has a permanent seat on it -- could block it.
Still, that's what former British Foreign Secretary David Owen urged world leaders to do before unleashing missiles or warplanes on Syrian targets.
Omran al-Zoubi, Syria's information minister, on Tuesday challenged the United States to "present this proof to the rest of the world" -- claiming that they are asking for trouble if they do not.
"If they don't have proof or evidence, then how are they going to stand up to the American public opinion and to the world public opinion and explain why they are attacking Syria?" al-Zoubi told CNN from Damascus.
Some worldwide have expressed concern that intervening in Syria may provoke broader conflict in the Middle East or ensnare Western powers in another bloody conflict after years of warfare in Iraq and Afghanistan.
Cameron said that he understands those concerns, vowing that any action would have to be "proportionate, ... legal (and) would have to be specifically about deterring the use of chemical weapons."
Still, he said it's critically important that action be taken to show the international taboo against chemical weapons will not be tolerated.
"This is not about wars in the Middle East; this is not even about the Syrian conflict," he said. "It's about use of chemical weapons and making sure, as a world, we deter their use and we deter the appalling scenes we've all seen on our television screens.