The US has vowed to take "appropriate action" in response to its assessment that an Iranian missile was responsible for downing a Ukrainian airliner, killing all 176 people on-board.

The crash came just a few hours after Iran launched a ballistic missile attack against Iraqi military bases housing American troops amid a confrontation with Washington over the US drone strike that killed an Iranian Revolutionary Guard general last week.

American and allied officials later said that they had intelligence that surface-to-air missiles fired by Iranian military forces shot down the Boeing 737 minutes after it took off from Tehran, headed for Kiev, the Ukrainian capital.

Video footage has also emerged showing the moment of impact. But Iran has so far denied any involvement in the downing of Ukrainian Flight 752.

US Treasury Secretary Steven Mnuchin and Secretary of State Mike Pompeo, held a joint press conference at the White House on Friday (local time) to address the Trump administration's next move, following Iran's attack on US military bases.

Mr Mnuchin and Mr Pompeo confirmed the US has imposed new sanctions on Iran, including penalties on the Islamic Republic's metals and some senior leaders.

The sanctions will target steel, aluminium, copper and iron, as well as eight senior Iranian officials and sectors of the economy, including construction, manufacturing, textiles and mining, they told reporters.

"We want Iran to simply behave like a normal nation," Mr Pompeo said at the White House.

The move to expand penalties on the Islamic Republic comes one day after US President Donald Trump said Iran would be sanctioned "immediately" for the air strikes against two US military installations in Iraq. There were no casualties.

Mr Mnuchin said that the US will also issue waivers on sanctions against Iran to allow American and other foreign investigators to take part in the probe of a Ukrainian jetliner crash in Tehran earlier this week.

American, British and Canadian officials say intelligence sources indicate that Iran shot down the plane, perhaps unintentionally, but this has been denied by Tehran.

During the press conference, Mr Pompeo confirmed for the first time that the US government believes Iran was "likely" to blame for the downing of a Ukrainian airliner that crashed shortly after takeoff in Tehran earlier this week.

"We do believe that it's likely that plane was shot down by an Iranian missile," he told reporters. "We're going to let the investigation play out before we make a final determination. It's important that we get to the bottom of it."

Mr Pompeo revealed that he spoke with his Canadian counterpart Justin Trudeau and with Ukrainian President Volodymyr Zelensky by phone on Friday.

"When we get the results of that investigation, I am confident we and the rest of the world will take appropriate action," he said.

Mr Zelensky said in a post on Facebook early Friday that the possibility a missile had downed the Ukraine International Airlines plane "cannot be ruled out but is not currently confirmed".

Hours later, Mr Zelensky's spokeswoman said the president had met with US Embassy officials in Kiev and received "important data that will be studied by our specialists" before he spoke with Mr Pompeo later in the day.

Victims of the crash included 82 Iranians, 63 Canadians and 11 Ukrainians as well as nationals from Sweden, the UK, Afghanistan and Germany.

Iran has promised a full investigation. However, TV images from the crash site on Thursday showed a mechanical digger helping to clear debris away, raising concerns that important evidence could have been removed.

Ukrainian experts have been given access to the black box flight recorders of the plane that crashed in Iran, Foreign Minister Vadym Prystaiko said on Friday, adding that they were receiving "full co-operation" from the Iranian authorities.

"Our team has now got access to the black boxes," Mr Prystaiko told a briefing. The Ukrainian experts had also been given access to the plane's fragments and the crash site, as well as recordings of the radio exchange between the pilots and traffic control, according to Mr Prystaiko.

"Conclusions - as soon as they are made - will be presented to the public," he said.

He said the plane's fragments had been scattered over a wide area including "certain settlements".

Speaking to reporters, Mr Prystaiko also stressed that all possibilities were under consideration.

"We are not rejecting any of the leads, all leads are being considered," he said.

"Our main task is to find the reasons of this tragedy in an absolutely just and unbiased manner.

"To find who is guilty if someone is guilty.

"But of course if we prove that this plane has been shot down we will of course demand that the guilty be brought to justice but also compensation."

Ukraine's top diplomat refused to say what kind of information Kiev had received from the West.

"This is secret information," he said.

megan.palin@news.com.au | @Megan_Palin