Obama considers options after Syria gas attack and consults UK’s Cameron

President Barack Obama and his top military and national security advisers hashed out options on Saturday for responding to the alleged use of chemical weapons in Syria amid “increasing signs” that the government used poison gas against civilians.

Obama spoke with British Prime Minister David Cameron, a top US ally, and agreed that chemical weapon use by Syrian President Syrian President Bashar al-Assad’s forces would merit a “serious response,” a spokesperson for the prime minister said in a statement.

Syrian opposition accounts that between 500 and well over 1,000 civilians were killed this week by gas in munitions fired by pro-government forces, and video footage of victims’ bodies, have stoked demands abroad for a robust, US-led response after two and a half years of international inaction on Syria’s conflict.

Syria sought to avert blame by saying its soldiers had found chemical weapons in rebel tunnels. US Secretary of State John Kerry called his Syrian counterpart on Thursday to chide the government for not allowing UN inspectors access to the site.

Obama has been reluctant to intervene in Syria’s civil war, but reports of the killings near Damascus have put pressure on the White House to make good on the president’s comment a year ago that chemical weapons would be a “red line” for the United States.

The United States is repositioning naval forces in the Mediterranean to give Obama the option for an armed strike.