U.S. officials said Friday that a U.S. military helicopter had crashed in western Iraq, killing all service members on board. CBS News understands there were seven U.S. troops on the aircraft when it went down, as first reported by the Associated Press late Thursday, after the crash. The U.S. military has not confirmed the death toll from the crash.

The statement issued Friday morning by the U.S.-led military coalition in Iraq said there was no immediate indication that the Pave Hawk helicopter was shot down.

The aircraft was being used by the Air Force for combat search and rescue, and was in transit from one location to another when it went down Thursday afternoon near al-Qaim in Anbar Province, where the U.S. has a base.

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"All personnel aboard were killed in the crash," said Brig. Gen. Jonathan P. Braga, director of operations, Combined Joint Task Force - Operation Inherent Resolve, in a written statement sent to CBS News. "This tragedy reminds us of the risks our men and women face every day in service of our nations. We are thinking of the loved ones of these service members today."

Our thoughts and prayers go out to the families and loved ones of the brave troops lost in the helicopter crash on the Iraq-Syria border yesterday. Their sacrifice in service to our country will never be forgotten. — Donald J. Trump (@realDonaldTrump) March 16, 2018

President Trump paid his respects to the fallen troops in a tweet, saying "their sacrifice in service to our country will never be forgotten."

The cause of the crash was under investigation.

Government officials in Baghdad told CBS News the Iraqi Army 8th division assisted U.S. forces to secure the crash site.

U.S. Defense Secretary James Mattis, who was traveling back to the U.S. from Bahrain, was briefed on the crash.

The U.S.-led coalition battling insurgents of the Islamic State of Iraq and Syria (ISIS) has an outpost in al-Qaim, which is located near the Syrian border. The anti-ISIS campaign accelerated through much of last year, as coalition and Iraqi forces battled to take back a string of cities and towns.

Prime Minister Haider al-Abadi declared victory over ISIS in Mosul in July. In the following months Iraqi forces retook a handful of other ISIS-held towns including Tal Afar in August, Hawija in September and Qaim in October. In November, Iraqi forces retook the last Iraqi town held by ISIS -- Rawah, near the border with Syria.

The U.S.-led coalition has continued to work with Iraq and Syrian Democratic Forces to shore up the border region to make sure that foreign fighters and insurgents can't move freely across the region.