ISTANBUL — The Turkish policeman who assassinated Russia’s ambassador was unlikely to have acted alone, a senior Turkish government official said yesterday, as investigators from both countries hunted for clues as to who might have been behind the killing.

Russian investigators arrived in Ankara yesterday attempting to uncover how off-duty policeman Mevlut Mert Altintas assassinated Moscow’s ambassador in an art gallery, as Turkey made its first arrests over the murder.

The senior government official described the killing as “fully professional, not a one-man action” and said the attack was well-planned. The official spoke on condition of anonymity because he was not authorised to release details to the press. Turkish authorities have not publicly released any information on the investigation or on a possible motive for the policeman.

Veteran diplomat Andrei Karlov was shot nine times in the back by Altintas, 22, in a brazen attack as he opened an exhibition of Russian photography late on Monday.

Members of the media present at the event captured the killing in graphic detail. Altintas, dressed smartly in a suit, necktie and white shirt, is caught in one photograph standing behind Karlov. In a video, Karlov is shown crumpling as he appears to be shot from behind.

As special forces stormed the building, Altintas initially waited by the ambassador’s body and would not allow him to be treated, Turkish media reported.

The killing stunned Ankara and Moscow, which have rowed repeatedly over the Syria conflict but in recent weeks have begun cooperating closely on the evacuations from war-torn Aleppo.

An unprecedented three-way meeting on Syria between the foreign ministers of Turkey, Russia and Iran in Moscow went ahead yesterday despite the assassination.

Adding to the jitters in a country already on high alert after a string of deadly attacks, an individual also fired outside the American Embassy in Ankara overnight Monday in a separate incident, prompting Washington to close its three diplomatic missions in the country for the day.

The mission said in a statement that no one was hurt, and that the individual had been detained.

“We have to know who directed the hand of the killer,” Russian President Vladimir Putin declared, and agreed with his Turkish counterpart Recep Tayyip Erdogan in an unprecedented move to send a Russian investigative team to the scene.

Dramatic images showed Karlov stumble, and then crash to the ground on his back as Altintas brandished his gun at terrified onlookers, who cowered behind cocktail tables at the Ankara gallery.

“Don’t forget Aleppo, don’t forget Syria. You will not be able to feel safe for as long as our districts are not safe. Only death can take me from here,” he shouted in Turkish.

Altintas also shouted that “We are the ones who swore allegiance to Mohammed for the jihad!”, which the mass-circulation Hurriyet newspaper said was a slogan commonly used in propaganda videos of the group formerly allied to Al Qaeda in Syria.

Altintas had set off the metal detector security check when he entered the exhibition in central Ankara as he was carrying a gun, according to Turkish media reports. But after showing his police ID, he was waved through.

Altintas, who had worked for Ankara’s anti-riot police for the last two-and-a-half years, was killed by the special forces after a 15-minute standoff. Six people have reportedly been detained over the attack, including his parents, sister, two relatives and a flatmate.

Ankara Mayor Melih Gokcek, known for his outspoken comments, speculated on Twitter that the gunman may be linked to the group of exiled Turkish cleric Fethullah Gulen, blamed for the July coup aimed at toppling Mr Erdogan.

Mr Gulen, who denies having any link to the failed coup, issued a statement condemning “in the strongest terms this heinous act of terror”.

The slogans that Altintas shouted suggested he was aligned to a radical Islamist ideology, rather than that of Mr Gulen, who preaches a message of interfaith dialogue.

Foreign Minister Mevlut Cavusoglu announced in Moscow that the street where the embassy is located would be named after the 62-year-old envoy.

Karlov was a career diplomat who began his career under the Soviet Union in 1976 and was notably Russia’s ambassador to North Korea from 2001-2006. He was posted to Turkey in 2013. AGENCIES