President Barack Obama said on Friday that the deployment of chemical weapons by the Syrian government was a “game changer” while noting that intelligence assessments proving that such weapons had been used were still preliminary.

“Horrific as it is when mortars are being fired on civilians and people are being indiscriminately killed, to use potential weapons of mass destruction on civilian populations crosses another line with respect to international norms and international law,” Obama told reporters at the White House.

“That is going to be a game changer. We have to act prudently. We have to make these assessments deliberately. But I think all of us … recognize how we cannot stand by and permit the systematic use of weapons like chemical weapons on civilian populations,” he said.

Obama was speaking during a meeting with Jordan’s King Abdullah in the Oval Office.

(Reuters)