A U.S. Army Apache helicopter gunship went down near the Strait of Hormuz on Monday, and the two crew members were safely rescued, according to two people briefed on the incident.

It was not immediately clear whether the Apache was shot down by Iranian fire, experienced mechanical failure or encountered some other problem, said one of the people, who spoke on the condition of anonymity and said the incident was under investigation.

The incident occurred after days in which hostilities in the region escalated and then ebbed, as Israel and Iran exchanged military strikes before stepping back, the latest example of the tenuous nature of the cease-fire.

The Trump administration had not disclosed news of the downed helicopter by the time The New York Times reached out to the White House press office for comment on Monday night.

A spokesman for President Trump did not immediately provide a statement about the incident. The military’s Central Command did not respond to a request for comment.

The U.S. military has used Apaches, as well as armed MQ-9 Reaper drones and F/A-18 and F-35 attack planes, as part of an aggressive effort by Central Command to challenge Iran’s effective closure of the Strait of Hormuz to most commercial traffic.

Iran has shot down about 30 unmanned Reaper drones, and a handful of U.S. fighter jets have been lost to hostile and friendly fire since the war started on Feb. 28. But this would be the first Apache lost in the conflict.

Last month, Central Command posted imagery on social media of Adm. Brad Cooper, the head of the command, flying over waters in or near the strait on the eve of an effort by the U.S. Navy to help guide commercial ships through the strait, a short-lived operation called Project Freedom.

The AH-64 Apache gunship, which is armed with Hellfire missiles, is one of the most fearsome types of aircraft operating in the region. They patrol the strategic waterway in part to deter small-boat attacks and to shoot down drones.

But the helicopters have been pushing closer to Iranian territory — including islands the Iranians control in the strait and the Persian Gulf — as part of the aggressive posture Central Command has maintained even as the United States and Iran have engaged in fitful negotiations to reopen the strait.

In response to Iran’s blockade, the United States imposed a blockade of its own on April 13, barring commercial vessels from entering or leaving an Iranian port. Since then, U.S. military ships have turned away 134 vessels.

The Navy has disabled seven other vessels that ignored American warnings to turn back, including a Palau-flagged oil tanker as it steamed through international waters in the Gulf of Oman toward Iran on Monday, Central Command said in a statement.

In April, two crew members of an F-15E Strike Eagle fighter jet shot down by Iran were rescued after ejecting from their stricken aircraft and landing deep in hostile territory.