Tehran, Iran: An engine of a Boeing 747 operated by Iran's Mahan Air detached from the plane Thursday shortly after takeoff from Tehran, causing terror among passengers but no injuries, local media reported.

The 747, with 300 passengers on board, was on a flight from the capital's Mehrabad airport to Bandar Abbas in southern Iran when one of its engines crashed into a nearby field, forcing the jumbo to return and make an emergency landing.

Iranian media and social networks carried pictures of the crashed engine.

Iran desperately wants to upgrade its ageing fleet of 140 operating aircraft, hamstrung by nuclear-related and other sanctions which have also made spare parts difficult to source.

The restrictions were partly lifted by an interim agreement on Iran's nuclear programme that came into force in January 2014.

This allowed for the sale of spare parts, although direct sales of aircraft remained banned.

A final accord reached in Vienna on July 14, expected to be implemented at the start of 2016, will lift the sanctions in exchange for putting curbs on Iran's nuclear programme.

Iran plans to buy Airbus and Boeing passenger planes through long-term payment agreements once the accord comes into effect, Transport Minister Abbas Akhoundi said last month.

To purchase new planes, "our negotiations have been mostly with Airbus and Boeing, and we have provided them with our plans and needs until 2020," he said.

In August, a civil aviation official said his country planned to buy 80 to 90 Airbus and Boeing planes a year until it has a new 300-strong fleet.