WASHINGTON — The United States is “on the verge” of ending Syria talks with Russia in response to days of deadly attacks on Aleppo, Secretary of State John Kerry said Thursday.

Kerry said such discussions make no sense at a time when Russian and Syrian warplanes are bombing rebel-held areas of Syria’s largest city. He said the U.S. has no indication of Russia’s “seriousness of purpose.”

Washington has been working with Moscow for months to try to secure a cease-fire in Syria. The latest truce collapsed last week after several days of relative calm.

Speaking Thursday at an event organized by The Atlantic magazine, Kerry outlined no new approaches for bringing peace to Syria. The Obama administration has made clear it won’t use military force against Syria’s government.

“We’re on the verge of suspending the discussion because it’s irrational in the context of the kind of bombing taking place,” Kerry said.

He appeared to offer Russia another last chance, however. “It’s one of those moments where we’re going to have to pursue other alternatives for a period of time, barring some clearer indication by the warring parties that they’re prepared to consider approaching this more effectively,” Kerry said.

This story corrects that Kerry spoke at an Atlantic magazine event, not at The Atlantic Council.