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WASHINGTON -- President Obama said on Saturday that he was ready to take military action against Syrian President Bashar Assad, but that he will seek the approval of Congress before carrying out a military strike.

Obama says Congressional leaders have agreed to schedule a debate and vote when they return to session. The president did not say if he'd forgo a strike if Congress disapproves.

"This attack is an assault on human dignity," Obama said. "It also presents a serious danger to our national security."

The remarks came amid a flurry of briefings for skeptical lawmakers by the president's national security team. The shouts from hundreds of activists outside the White House protesting against military action could be heard from the Rose Garden shortly before Obama spoke.

The remarks come hours after U.N. experts, who had been collecting samples from last week's alleged chemical weapons strike outside Damascus, left the country bound for the Netherlands.

The chemical weapons experts were working to determine what occurred in the apparent chemical weapons attack near Damascus on Aug. 21, which U.S. intelligence reports say left 1,429 people dead, including 426 children. They have taken blood and urine samples from victims and soil samples from areas where chemical attacks have been reported. The samples will be tested in Europe.