U.S. Seeks Meeting to Avert Ukraine Attack

WASHINGTON—Secretary of State Antony Blinken warned of a looming Russian offensive against Ukraine and proposed a last-ditch diplomatic meeting with his Russian counterpart next week that he said could lead to a summit of key leaders.

Mr. Blinken spoke at a United Nations Security Council meeting Thursday just hours after Russia told the U.S. in a formal document that it might resort to “military-technical measures” if it didn’t receive legally binding security assurances.