"It is very troublesome. That starts getting to some core national interests that the United States has, both in terms of us making sure that weapons of mass destruction are not proliferating, as well as needing to protect our allies, our bases in the region," he said, without offering any indication of how the United States might respond.
On Thursday, Secretary of State John Kerry called his Russian counterpart Sergei Lavrov, according to a Russian Foreign Ministry statement. The two discussed Syria and agreed on the need for an "impartial" investigation into the latest alleged chemical weapons attack, the statement said.
American and Russian officials are set to meet next week to discuss plans for a long-delayed conference on Syria, which hopes to bring both the Assad government and the rebel groups to the table.