(CNN) - Vice President Joe Biden declared Tuesday "there is no doubt" that the Syrian government is responsible for alleged chemical weapons use and that he has been in touch with foreign leaders as the U.S. contemplates a military response.
"There is no doubt that an essential international norm has been violated," he said in Houston at the American Legion National Convention. "No one doubts that innocent men women and children have been the victims of chemical weapons attacks in Syria and there is no doubt who is responsible for this heinous use of chemical weapons in Syria: the Syrian regime."
His comments come as U.S. officials are preparing for a potential military strike against Syria following the suspected August 21 chemical weapons attack that killed some 1,300 people near Damascus.
Secretary of State John Kerry said Monday there was "little doubt" that al-Assad's government was responsible for the chemical weapons use.
"What we saw in Syria last week should shock the conscience of the world. It defy it defies any code of morality," Kerry said.
United Nations investigators visited that site Monday, but are not tasked with determining who used chemical weapons, only whether or not they were used.
The Russian government has cautioned the U.S. against jumping to conclusions, and Syria's information minister told CNN on Tuesday the U.S. should put their cards on the table.
"If the United States Administrations has proof that we used chemical weapons, than they should present this proof to the rest of the world," Omran al-Zoubi said in an interview with CNN's Frederik Pleitgen. "If they don't have this proof or evidence, then how are they going to stand up to American public opinion and world public opinion and explain why they are attacking Syria."
Biden said Tuesday that he and Obama "believe that those who use chemical weapons against defenseless men women and children should and must be held accountable.
White House spokesman Jay Carney said Tuesday that the Obama administration is not considering whether weapons were used or by whom, but deciding "the question of what's the appropriate response to this clear violation of international norms."