FILE - The USS Abraham Lincoln carrier and a U.S. Air Force B-52H Stratofortress, conduct joint exercises in the U.S. Central Command area of responsibility in Arabian Sea June 1, 2019. The warship has now been deployed near the coast of Iran in the event of an outbreak of war.

DUBAI, United Arab Emirates — Iran conducted military drills with Russia on Thursday as a second American aircraft carrier drew closer to the Middle East, with both the United States and Iran signaling they are prepared for war if talks on Tehran’s nuclear program fizzle out.

President Donald Trump said he believes 10 to 15 days is “enough time” for Iran to reach a deal. But the talks have been deadlocked for years, and Iran has refused to discuss wider U.S. and Israeli demands that it scale back its missile program and sever ties to armed groups.

Indirect talks in recent weeks made little visible progress, and one or both sides could be buying time for final war preparations.

Iran’s theocracy is more vulnerable than ever following 12 days of Israeli and U.S. strikes on its nuclear sites and military last year, as well as mass protests in January that were violently suppressed.

In a letter to the U.N. Security Council on Thursday, Amir Saeid Iravani, the Iranian ambassador to the U.N., said that while Iran does not seek “tension or war and will not initiate a war,” any U.S. aggression will be responded to “decisively and proportionately.”

“In such circumstances, all bases, facilities, and assets of the hostile force in the region would constitute legitimate targets in the context of Iran’s defensive response,” Iravani said.

Earlier this week, Iran launched a drill that involved live-fire in the Strait of Hormuz, the narrow opening of the Persian Gulf through which a fifth of the world’s traded oil passes.

The movements of additional American warships and airplanes, with the USS Gerald R. Ford aircraft carrier near the mouth of the Mediterranean Sea, don’t guarantee a U.S. strike on Iran — but it bolsters Trump’s ability to carry out one should he choose to do so.

He has so far held off on striking Iran after setting red lines over the killing of peaceful protesters and mass executions, while reengaging in nuclear talks that were disrupted by the war in June.

Iran has agreed to draw up a written proposal to address U.S. concerns raised during this week’s indirect nuclear talks in Geneva, according to a senior U.S. official who was not authorized to comment publicly and spoke on the condition of anonymity.

The official said top national security officials gathered Wednesday to discuss Iran, and were briefed that the “full forces” needed to carry out potential military action are expected to be in place by mid-March. The official did not provide a timeline for when Iran is expected to deliver its written response.

“It’s proven to be, over the years, not easy to make a meaningful deal with Iran, and we have to make a meaningful deal. Otherwise, bad things happen,” Trump said Thursday. He added Iran has about 10 to 15 days to reach a deal.