DAMASCUS, Syria (AP) — Syria on Tuesday said U.S. Secretary of State John Kerry was lying when he stated there was "undeniable" evidence of a large-scale chemical attack likely launched by Damascus, accusing him of disregarding the work of U.N. investigators.

On Monday, Kerry used tough language to refer to an alleged poison gas attack in Damascus last week, saying that an "international norm cannot be violated without consequences."

The remarks were the clearest justification yet for U.S. military action in Syria, which, if President Barack Obama decides to order, most likely would involve sea-launched cruise missile attacks on Syrian military targets.

Support for some sort of international military response was likely to grow if it is confirmed that Assad's regime was responsible for the Aug. 21 attack in the Damascus suburbs that activists say killed hundreds of people. The group Doctors Without Borders put the death toll at 355.

Obama has not decided how to respond to the purported use of deadly gases in the attack, but appeared to be moving ahead even as a United Nations team already on the ground in Syria collected evidence from the attack.

The Syrian statement published Monday on the state-run Syrian Arab News Agency, which acts as a government mouthpiece, said Kerry's insistence on "jumping over" the work of U.N. experts in Syria shows that the U.S. has deliberate intentions to exploit events.

It said Kerry has also "fabricated" evidence by accusing the Syrian government of non-cooperation with the U.N. delegation and of delaying their arrival to the sites that were allegedly attacked by chemical weapons.

The U.N. team traveled Monday to the western Damascus suburb Moadamiyeh, one of the areas affected by the purported chemical attack, where they collected samples and testimony after a treacherous journey through government and rebel-held territory. Their convoy was hit by snipers but members of the team were unharmed.

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U.N. Secretary-General Ban Ki-moon said he had instructed U.N. disarmament chief Angela Kane in Damascus "to register a strong complaint" with both the Syrian government and opposition representatives for the convoy attack.

U.N. spokesman Farhan Haq said the team plans to go out again Tuesday to do more sampling, and activists said the team was expected in the eastern suburbs of Zamalka and Ein Tarma.

An Associated Press photographer outside the team's hotel in Damascus said he saw Kane and Swedish chemical weapons expert Ake Sellstrom leave the hotel heading to an undisclosed location, while the remaining inspectors stayed behind.