The Ukrainian plane crash that killed 176 people likely won’t be investigated by Boeing or the National Transportation Safety Board, according to senior U.S. investigative sources.

While international agreements allow the NTSB and the U.S. company to assist on any overseas crash involving a Boeing aircraft, the sources told NBC News that current hostilities with Iran and the U.S. sanctions against that country are expected to prohibit U.S. teams from assisting Iranian investigators.

The Ukrainian International Airlines crash comes as President Donald Trump announced further sanctions against Iran in response to the Tuesday evening retaliation by Tehran for the killing of Gen. Qassem Soleimani, head of the Quds Force.

The NTSB said Wednesday it is monitoring the crash, and “is following its standard procedures for international aviation accident investigations, including long-standing restrictions under the country embargoes.”

The aviation board said it is working with the Department of State and other government agencies to determine the “best course of action.”

Handover of the black box would be standard protocol in any crash, and Iran could send the boxes to a third country, such as France, to read out the cockpit voice and flight data recorders.

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Boeing called the crash “tragic” and offered its condolences to the victims and their families. “We are in contact with our airline customer and stand by them in this difficult time. We are ready to assist in any way needed,” the company said in a statement Wednesday.

The plane involved is a newer Boeing 737-800 series, which is not among the 737 Max planes that have been grounded since last March, following two fatal crashes overseas killing 346 people.

In both Indonesia and Ethiopia, NTSB and Boeing investigators were on the ground following those Max crashes looking for clues and assisting local investigators.

Investigators in Wednesday’s crash would be looking for any signs that a mechanical problem or a missile or a bomb brought down the Ukrainian plane.

U.S. aviation sources question why Iran had allowed commercial air traffic to depart Tehran, shortly after the country launched missiles against U.S. targets in Iraq.

It remains unclear how the plane went down, but video from the crash site showed what appeared to be pieces of an aircraft fuselage, an engine and other debris on the outskirts of Iran’s capital.

Iranian state TV said mechanical issues were suspected to have caused the crash, but Ukrainian officials said it was too early to determine the cause.

According to Ukrainian Foreign Minister Vadym Prystaiko, 82 people on board the flight were Iranian, 63 Canadian and 11 Ukrainian, including the nine crew members. Ten were from Sweden, four from Afghanistan, three from Germany and three from the United Kingdom. There were no survivors.

Meanwhile, some of the families of the Max crash in Ethiopia released a statement reacting to the news of the crash.

”What a sad day. What sad news. When shall we wake up from this nightmare?” the families said through a lawyer. “The news is heartbreaking after almost 10 months of feeling the loss of our families. Some of us don’t even know how to feel about this news.”

Paul Njoroge of Canada who lost his entire family in the crash of the Boeing jet on March 10 in Ethiopia said the news of the Ukrainian airline crash “brought a chill in my entire body.”

“I know and feel the pain of losing loved ones in such a tragic manner. My sincere condolences goes to the families who lost loved ones in the crash of PS752,” Njoroge said.

Ben Kesslen contributed.

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