Rescue workers and forensic investigators inspect the bodies of victims of a Ukrainian plane crash. airport, killing all onboard.

Iran has formally invited the U.S. National Transportation Safety Board to take part in its investigation into the crash of a Ukrainian jetliner and the U.S. agency has agreed to assign an investigator, an Iranian official said on Thursday.

"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.

The NTSB declined comment.

A person briefed on the matter confirmed the NTSB had agreed to take part but said it was unclear what if anything its representative would be able to do under U.S. sanctions.

The United States is allowed to take part under global rules since the Boeing 737-800NG jet was designed and built there.

Boeing said in a statement that it was "supporting the NTSB in the accident investigation." Iran's IRNA news agency also quoted a Foreign Ministry spokesman as saying Iran "has invited both Ukraine and the Boeing company to participate in the investigations."

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.