Republican Sen. Lindsey Graham said the United States should be prepared to send troops to Syria to secure that nation's chemical weapons.
The South Carolina lawmaker's warning comes after a recent report claiming Syria has used a chemical weapon in it's civil war.
But Syria's government accused rebels of firing a chemical weapon on the town of Aleppo, Tuesday.
"If today's reports are substantiated, the president's red line has been crossed, and we would urge him to take immediate action to impose the consequences he has promised," Sens. Graham and John McCain, R-Ariz., wrote in a joint statement Tuesday.
Israel's new minister of intelligence and strategic affairs said it's "apparently clear" that either the government or rebel forces fired a chemical weapon.
A U.S. official said there is no evidence to support that claim. However, he said the United States is ready to respond if Syria crosses that "red line" for intervention.