Pressure on the Obama administration to use military force in Syria intensified Tuesday after reports that President Bashar Assad’s government had crossed a line drawn by President Obama by using chemical weapons.

The reports, which were denied by the Syrian government and unconfirmed by third parties, triggered a growing number of lawmakers to call on the White House to at least arm the rebels fighting Assad.

Sen. Lindsey Graham (R-S.C.) said not acting decisively to secure chemical weapons sites would leave the United States looking like a “paper tiger.”

“I’ve never been more worried about weapons of mass destruction falling into terrorists’ hands than I am right now,” he said. “And I would urge the president and Republican leaders to openly embrace ending this conflict sooner rather than later with a post-Assad plan that focuses on securing these chemical weapons sites.”