Ukraine, US officials offer theories behind crash in Iran, as Trump says he has 'terrible feeling' about disaster.

New Zealand is joining calls for an independent and unimpeded investigation into the crash of an airliner shortly after takeoff from the Iranian capital Tehran, killing all 176 people on board.

Speculation is mounting the Ukraine International Airlines Boeing 737-800 - travelling from Tehran to Kyiv in Ukraine - was shot down by an Iranian anti-aircraft missile.

Acting Prime Minister and Minister of Foreign Affairs Winston Peters said on Friday that developments suggesting a surface-to-air missile was responsible for downing the plane was "disastrous news".

"New Zealand offers its deepest sympathies to the families of the 176 victims. It is a tragic loss of life for all countries involved," Peters said in a statement.

READ MORE:

* Video appears to show missile hitting passenger jet over Iran

* Iran investigators say Ukrainian flight never called for help, tried to turn back before crash

* 'Airplanes don't just catch fire': Iran jet crash leaves mystery with probe curbed by US tensions

RED CRESCENT/ TWITTER Iran's Red Crescent Organisation tweeted this image of the apparent crash site of the Ukrainian plane.

"We join others in calling for a thorough, independent and unimpeded investigation into the circumstances of the crash."

Of the 176 people who died in the crash of flight PS752, 63 were Canadians, while in total 138 of the passengers were destined for Canada, which is home to a large Iranian community.

Peters said New Zealand, through this country's embassy in Tehran, had offered help to Canada, which does not have an embassy in Iran, in its consular response to the crash.

Commenting on tension in the region between the US and Iran, Peters said the region had calmed in the past 24 hours but remained unstable. "We continue to call for diplomacy at this time of heightened tensions," he said.