(Adds NTSB statement)
PARIS, Jan 10 (Reuters) - The U.S. National Transportation Safety Board (NTSB) has accepted an invitation from Iran to take part in its investigation into the crash of a Ukrainian airplane in Tehran, the agency confirmed late on Thursday.
The NTSB said in a statement its Response Operations Center had received formal notification from Iran of Wednesday's crash of the Boeing 737-800 that killed all 176 on board. "The NTSB has designated an accredited representative to the investigation of the crash," the agency said.
The NTSB confirmed it would take part in the probe after an Iranian official told Reuters of the agreement.
"The NTSB has replied to our chief investigator and has announced an accredited representative," Farhad Parvaresh, Iran's representative at the International Civil Aviation Organization, part of the United Nations, told Reuters.
A person briefed on the matter said it was unclear what if anything its representative would be able to do under U.S. sanctions. NTSB said in its statement it "continues to monitor the situation surrounding the crash and evaluate its level of participation in the investigation."
The United States is allowed to take part under global rules since the Boeing 737-800NG jet was designed and built there.
Canada, which had dozens of passengers onboard, has also assigned an expert, while a team from Ukraine held discussions in Tehran on Thursday, Parvaresh said in a telephone interview.
Iran is ready to provide consular facilities and visas for accredited investigators, he added.
Sweden and Afghanistan, which had some passengers on board, have also been notified. France may also be involved as it was one of the countries where the engines were made, Parvaresh said.
He denied U.S. and Canadian claims that the jet had been shot down accidentally and said Iran was committed to a full and transparent investigation for the accident, adding it was too early to speculate on the cause.
"As Iranians we feel this tragedy and disaster for us and for the families," Parvaresh said, expressing condolences to the relatives of the people who died.
Canadian Prime Minister Justin Trudeau said earlier the jet was probably brought down by an accidental Iranian missile strike, citing intelligence from Canadian and other sources.
The U.S. government believes Iran shot down the plane by mistake, three U.S. officials told Reuters.
The Ukraine International Airlines flight to Kiev from Tehran crashed hours after Iran fired ballistic missiles at two U.S. military bases in Iraq.
Parvaresh said expert testimony indicated that the aircraft could not have been hit by a missile and that it was important to keep the crash investigation non-political.
"I think we should keep this purely technical and not confuse it with political tensions in the region. We should leave it to experts to investigate and make their report." (Reporting by Tim Hepher; additional reporting by DAvid Shepardson in Washington Editing by Chris Reese, Lisa Shumaker and Raju Gopalakrishnan)