ANKARA (REUTERS) - The 22-year-old Turkish policeman who gunned down the Russian ambassador in Ankara called in sick on the day of the attack and promised to bring a doctor's note for his supervisors, a senior security official told Reuters.

The government has identified Mevlut Mert Altintas as the gunman who shouted "Don't forget Aleppo!" and "Allahu Akbar" as he opened fire repeatedly on envoy Andrey Karlov while he was giving a speech at an art gallery in the Turkish capital.

The attack, caught on video and widely circulated on social media, was a grisly reminder of the spillover faced by both Turkey and Russia from the Syrian civil war, where they are on opposing sides and where Russian-backed Syrian forces last week ended rebel resistance in the northern city of Aleppo.

On Monday (Dec 19) morning, Altintas called the division of the Ankara riot police where he had worked for 2-1/2 years and said he was unwell and would bring a doctor's note upon his return, the official said.

Altintas, who lived in a shared flat in the Demetevler neighbourhood on the outskirts of Ankara, spent the night before the attack at a hotel in central Ankara close to the gallery, the official said.

"He walked from the hotel ... to the gallery. He showed his police ID at the entrance," the official said.

This allowed him to bypass a security check and bring his gun into the venue.

SMARTLY DRESSED

Karlov was speaking at an event for the gallery's showing of an exhibition of photos from Russia, entitled "From Kaliningrad to Kamchatka". Media present captured the killing in graphic detail.

In one photo, Altintas - dressed smartly in a suit, necktie and white shirt - is seen standing just behind Karlov as the ambassador spoke. In a video from moments later, Karlov is shown crumpling as he appears to be shot from behind.

Altintas fired some 11 shots with nine of those hitting Karlov, the official said, citing the initial police report. Photographs from the incident showed a wall marked by what appeared to be gunfire.

Turkish special forces stormed the gallery and gunfire was heard for some time after, according to a Reuters cameraman at the scene. As they entered the building, Altintas initially waited by the ambassador's body and would not allow him to be treated, the Hurriyet newspaper reported.

A source familiar with the gallery said Altintas was spotted at the exhibition on the opening night, the Friday before the attack.

"There was a ceremony for the opening of the exhibition on Friday evening and the attacker came to that event," the person said. "Probably he was doing reconnaissance."