Bloomberg� - Iran has invoked an international agreement to get assistance from foreign investigators�including from the U.S.�in the investigation of Wednesday�s fiery crash of a jetliner near Tehran, according to two people familiar with the matter.

Such a move is common in aviation disasters, and gives the country where the plane was produced the ability to participate. The plane that crashed was a U.S.-built Boeing Co. 737-800.

However, American agencies including the National Transportation Safety Board are weighing whether it is legal to engage with Iranian authorities under the terms of sanctions the U.S. has imposed on Iran. Moreover, they are concerned about the safety of sending people there given the confrontation between the two countries that has led to military strikes on both sides, the people said.

The probe into Ukraine International Airlines Flight 752 -- which plunged from the sky minutes after takeoff, killing all 176 people aboard -- is fraught with difficulty and intrigue.

The crash came hours after an Iranian missile attack on two Iraqi military bases in retaliation for an American drone attack last week that killed one of Iran�s top generals. American forces are stationed at both bases.

Under the United Nation�s International Civil Aviation Organization, crash investigations are conducted by the nation in which they occur. In addition, the country where the plane and key components are manufactured are allowed to take part.

Iran notified the UN agency of the accident in the hours after it occurred, according to the people, who were briefed on the matter but weren�t authorized to speak about it and asked not to be named.

The NTSB routinely participates in dozens of crash investigations around the world under the ICAO process, known as Annex 13.

By notifying the ICAO, Iran suggested it might be open to U.S. help in the probe, said the two people. But the Islamic Republic has sent mixed signals, with some officials being quoted as saying they would not allow Americans to analyze the plane�s two crash-proof flight recorders, for example.

American law also prohibits the NTSB from working in Iran because of longstanding bans on conducting business in that country. The NTSB has occasionally assisted in accident investigations there, but had to obtain special permission from the U.S. Treasury. The process of obtaining such approval has at times taken more than a year.

�The NTSB is monitoring developments surrounding the crash of Ukraine International flight 752 and is following its standard procedures for international aviation accident investigations, including long-standing restrictions under the country embargoes,� the agency said in an emailed statement Wednesday.

�As part of its usual procedures, the NTSB is working with the State Department and other agencies to determine the best course of action.�

The State Department issued a statement offering assistance to Ukraine, but notably didn�t mention helping Iran. �The United States calls for complete cooperation with any investigation into the cause of the crash,� the department said.

The aircraft climbed normally until it reached an altitude of 7,900 feet (2,408 meters), then suddenly stopped transmitting its position, according to data from the tracking site FlightRadar24.

The jetliner was equipped with a device that communicated with the airline and it also showed the plane was behaving normally until it stopped transmitting at about the same time, said a person familiar with the data.

The airline said in a statement that the investigation would include representatives of Iran, Boeing, the airline and the National Bureau of Air Accidents Investigation of Ukraine.

Boeing said in a statement �we are ready to assist in any way needed.�