LUCCA, Italy (AP) — U.S. Secretary of State Rex Tillerson says Russia must choose between aligning itself with the U.S. and likeminded countries or embracing Syrian President Bashar Assad, Iran and the militant group Hezbollah.

Tillerson says it's unclear whether Russia failed to take seriously its obligations in Syria or has been incompetent. But he says that distinction "doesn't much matter to the dead."

He says of the recent chemical attack: "We cannot let this happen again."

Tillerson says the U.S. sees no future role for Assad in Syria, but he says the U.S. isn't pre-supposing how Assad's departure will occur.

Tillerson is traveling Tuesday to Moscow. He says Russia can play a role in Syria's future but that aligning with Assad won't serve Russia's long-term interests.