Theresa May has said the shooting of the Russian ambassador to Turkey is “a matter of concern”.
Foreign Secretary Boris Johnson also left the chamber immediately after the Prime Minister’s announcement in the Commons.
During a statement about last week’s European Council, Mrs May told MPs: “I was just looking at what I believe, Mr Speaker, is some breaking news that the Russian ambassador to Turkey has been shot, which is a matter which has yet to be confirmed, but I think is a matter of concern.”
The ambassador, Andrei Karlov, was several minutes into a speech at an exhibition in the Turkish capital Ankara when a man - believed to be a police officer - wearing a suit and tie shouted “Allahu Akbar” and fired at least eight shots, according to an Associated Press photographer in the audience.
The attacker also said some words in Russian and smashed several photos which were part of the exhibition.
Russian foreign ministry spokeswoman Maria Zakharova said in a televised statement that the ministry would soon comment on “the attack on the Russian ambassador in Turkey”.
Mr Johnson later condemned the “cowardly” and “despicable” murder of Russia’s ambassador to Turkey Andrei Karlov.
It was revealed Turkish police fatally shot the gunman, NTV reported.
The attacker also smashed several of the photos which were part of the exhibition.
There was panic as people ran for cover after the shots were fired, with three other people reportedly wounded in the attack.
Ms Zakharova said Mr Karlov was shot “when an unidentified assailant opened chaotic gunfire during a public event in Ankara”.
She later confirmed the ambassador had died, adding that Russia was in contact with Turkish officials about the incident.
Ankara mayor Melih Gokcek told reporters outside the exhibition centre that the “heinous” attack had aimed to disrupt newly-re-established relations between Turkey and Russia.
US state department spokesman John Kirby said US officials are aware of reports about the shooting.
“We condemn this act of violence, whatever its source,” Mr Kirby said. “Our thoughts and prayers are with him and his family.”
Mr Karlov, 62, joined the diplomatic service in 1976, and went on to serve as Russia’s ambassador to Pyongyang from 2001-2006.
He later worked as the chief of the foreign ministry’s consular department, and had been Russia’s ambassador to Turkey since 2013.
Meanwhile, a truck has run into crowded Christmas market in Berlin; causing multiple injuries, according to reports.