WASHINGTON -- President Barack Obama said the United States is seeking corroboration of intelligence that Bashar Assad's regime in Syria used chemical weapons in that country's civil war, reiterating that confirmation would be a "game-changer" for the U.S. response.

Speaking before a private White House meeting with Jordan's King Abdullah II, Obama repeated the language the administration used Thursday that intelligence agencies have "varying degrees of confidence" in evidence that chemical munitions were used against Assad's opponents.

"There are a range of questions around how, when, where these weapons may have been used," Obama said Friday. "We have to make these assessments deliberately, but I think all of us -- not just in the United States, but around the world -- recognize how we cannot stand by and permit the systematic use of weapons like chemical weapons on civilian populations."

In his first public remarks since the United States disclosed it has evidence that chemical weapons were used in Syria, Obama didn't specify how the United States might respond.

In Damascus, information Minister Omran al-Zoubi said that "the fabricated and false" allegations "do not have any credibility," according to the official Sana news agency. The regime has said that chemical weapons have been used by terrorists, its blanket description for the opposition.

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A Syrian official speaking on condition of anonymity accused opposition forces of using the weapons in a March attack on the village of Khan al-Assal outside of the northern city of Aleppo.

Obama is under pressure from some members of Congress to take stronger action in Syria following U.S. intelligence assessments that sarin nerve gas may have been used in the conflict. The administration has resisted providing arms to the rebels or taking direct military action.

The White House informed lawmakers that U.S. intelligence agencies have concluded "with varying degrees of confidence" that Assad's regime has used small amounts of sarin nerve gas.