President Donald Trump said Tuesday that Iran shot down an American Apache attack helicopter near the Strait of Hormuz Monday night, and that the United States would respond to the attack.

Trump has fought to hold together a fragile ceasefire between Iran, Israel, and the U.S. for more than a month, even amid renewed attacks from both of the other countries.

“I have just been informed by our Great Military that last night the Iranians shot down one of our highly sophisticated Apache Helicopters while patrolling over the Strait of Hormuz,” the president wrote on Truth Social Tuesday afternoon. “There were two pilots involved, both are safe and uninjured. Nevertheless, the United States must, of necessity, respond to this attack.”

Earlier in the day, U.S. Central Command confirmed the downing of the American helicopter but said that the government was still conducting an investigation into who was responsible.

Fox News, citing two U.S. officials, reported that the Apache was downed by an Iranian suicide drone.

An American Navy drone was also used in the operation to rescue the two American pilots, according to CENTCOM.

“The surface drone that assisted in last night’s rescue off the coast of Oman was a U.S. Navy Corsair unmanned surface vessel operated by U.S. 5th Fleet’s Task Force 59,” CENTCOM spokesman CAPT. Tim Hawkins told the Washington Examiner, explaining that the operation task force had been using the drones since March. “The drone picked them up and transported them to another location on the water where they were then hoisted up to a helicopter for further transport.”

Iran launched strikes at U.S. military bases in Kuwait earlier this month that resulted in no casualties, following a series of what the president described as “skirmishes.”

The president previously said that nothing short of new American casualties caused by Iranian attacks would break the shaky ceasefire, but White House officials did not immediately say if Trump’s statement was meant to indicate a new phase in the war.

John Ullyot, Trump’s first term National Security Council spokesman, told the Washington Examiner that Trump would be sitting on a “menu of options” for a military response compiled by Chairman of the Joint Chiefs of Staff Dan Caine, CENTCOM Commander Brad Cooper, and the rest of his national security team.

“That is the job of the joint staff, together with the, together with the combatant commanders,” he said Tuesday. “The joint staff make sure the commbatant commanders have target lists and options for the president to respond. They can always be tweaked, but in general, there are many options based on what assets are in the region, and a bunch of other factors.”

Ullyot noted that Trump “made attacks on U.S. military assets a red line for him when it comes to something that’s acceptable from the Iran” but added it’s hard to tell whether it’s going to be just a one time response or if it’ll be a lot bigger.”

Despite Trump’s diplomatic efforts, fighting in the Iranian conflict has surged in recent days.

Over the weekend, Hezbollah, an Iranian proxy group operating near Beirut, Lebanon, fired rockets at targets in Israel. Israel responded in turn with strikes on Hezbollah command outside of Beirut, which prompted both Iranian strikes against Israel and a new wave of retaliatory attacks launched by Israel.

Throughout it all, Trump had urged leaders to stop their attacks both in public and through diplomatic channels. The president spoke with Israeli prime Minister Benjamin Netanyahu multiple times this week, but he told reporters that, by the time he spoke with his counterpart Monday morning, Israeli rockets were already in the air.