The United States remains willing to negotiate an end to the US-Iran conflict, US Secretary of State Marco Rubio said on Wednesday during a meeting with Southeast Asian foreign ministers in Manila.

Washington was "always committed to diplomacy" but doubted whether Tehran was equally committed to negotiations, Rubio said.

"The problem we're having right now is that they're not serious about talks. If they're serious, we're serious. If they're not, then we will do what's necessary to protect our interests, and also the interests of our allies," he said.

Iran did not immediately respond to Rubio's comments.

A senior Iranian official told Reuters on Monday that Tehran had received a proposal from mediators for a 10-day ceasefire in efforts to salvage the interim ceasefire agreement signed by the US and Iran in June, which replaced an earlier April ceasefire.

In another sign that diplomacy remains alive, a high-level Iranian delegation led by Interior Minister Eskandar Momeni visited mediator Pakistan on Tuesday as tensions between Iran and the United States continued to escalate.

With no diplomatic breakthrough in sight, the US military bombed targets across Iran for an 11th straight night on Tuesday. Tehran residents reported hearing explosions in the early hours of Wednesday as Iran activated ‌its air defenses over the capital, Iran's semi-official Fars news agency said.

Three locations in Iran's Bushehr Province, home to Iran's only nuclear power plant, were hit by US attacks early on Wednesday, an official told Iran's state news agency IRNA, including an electricity post close to the plant.

Iran's army said it targeted US military facilities in Kuwait, Jordan and Bahrain with drones early on Wednesday. The army said it struck accommodation buildings and equipment storage facilities at Al Azraq air base in Jordan, and later targeted equipment warehouses and aircraft maintenance hangars at Sheikh Isa Air Base in Bahrain using Arash suicide drones.

US President Donald Trump confirmed that 18 US service members had been killed so far in the war, including four in Iranian attacks on US military bases in Jordan and Iraq over the last few days.

Oil prices rose further in Asian trade on Wednesday after climbing more than 2% on Tuesday following the Houthi threats, with Brent crude hovering above $91 a barrel and US gasoline back over $4 a gallon.

(With input from Reuters)