A helicopter belonging to an international peacekeeping force crashed in Egypt's Sinai peninsula on Thursday, killing at least eight people, including five Americans, the force confirmed.
The MFO originally said six U.S. service members had died but later said one of the six had survived.
"During a routine mission in the vicinity of Sharm el-Sheikh, Egypt, nine members of the Multinational Force and Observers (MFO) were involved in a helicopter crash," the MFO said in a statement.
Acting Defense Secretary Christopher Miller confirmed that Americans had been killed and said in a statement that he was "deeply saddened" by the deaths.
"Yesterday we recognized the sacrifice of millions of American veterans who have defended our nation for generations, and today we are tragically reminded of the last full measure our uniformed warriors may pay for their service," he said. "I extend the Department’s condolences to the families, friends and teammates of these service members.”
The Czech Defence Ministry released a statement confirming a Czech army member was among those killed in the helicopter crash. The statement said the cause of the crash was a technical fault.
The MFO, an internationally recognized observer mission, said one U.S. member survived. The victims' names are being withheld while their families are informed.
"At this point, there is no information to indicate the crash was anything except an accident," the MFO said.
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"I send my sincere condolences to the families of those killed and wish a speedy recovery to the wounded," Israeli Foreign Minister Gabi Ashkenazi said in a statement posted on Twitter.
"The contribution of the Multinational Force and Observers to maintaining security and stability in the region is extremely important, and I would like to express my gratitude to the countries that are contributing to the security and peace between Israel and Egypt."
A spokesperson for the Israel Defense Forces told NBC News that Israel had offered to help evacuate the wounded and that specialized medical teams could be mobilized if needed. An injured American was taken by helicopter to an Israeli hospital for medical treatment, they added.
According to its website, the MFO has 1,154 military personnel from the U.S. and 12 other countries covering an area of more than 3,860 square miles in the Sinai. Some 452 of its personnel are American.
In recent years, Washington has been assessing to what extent the U.S. should participate in the MFO, especially as military coordination between Israel and Egypt has tightened to help beat back an Islamist-led insurgency in the Sinai.
The force's responsibilities include monitoring troop levels along the border and ensuring the freedom of navigation through the Strait of Tiran.
The MFO was installed to monitor the demilitarization of the Sinai under a 1979 Egyptian-Israeli peace accord.
Reuters and the Associated Press contributed to this story.