UN Secretary-General Kofi Annan has expressed his sadness over the crash of an Iranian passenger plane earlier on Friday, a UN spokesman said Friday.

"The secretary-general was deeply saddened to learn of the deaths of passengers in a plane crash in Mashhad, Iran," said the spokesman in a statement.

"On the eve of his visit to the country, the secretary-general's thoughts are with the families of the victims of this tragedy. He extends his sincere condolences to them and to the Government of Iran," said the statement.

Twenty-nine people died Friday when a Tupolev 154 domestic jetliner burst into flames after landing in the northeastern city of Mashhad, Iranian authorities said.

Annan, currently on a tight-scheduled Mideast tour, plans to travel to Iran on Saturday where he is expected to meet with President Mahmoud Ahmadinejad and Foreign Minister Manouchehr Mottaki.

The visit comes two days after a UN deadline for Iran to halt nuclear enrichment activities which the West sees as a disguised bid to develop a nuclear bomb. Iran has insisted its nuclear program serves only civilian and peaceful ends.