UPDATE 1:13 p.m. EST: A memorial for Karlov is underway.
Russian investigators are in Ankara to probe the assassination of Andrei Karlov, Russia's ambassador to Turkey. Turkish police have detained seven people with ties to the gunman Mevlut Mert Altintas, including his parents, sister, roommate and three other relatives.
A previously scheduled meeting between Turkey and Russia to discuss the war in Syria continued as planned.
US Embassy in Ankara and Consulates Istanbul and Adana closed for normal operations today. Visa appointments will be rescheduled.— US Embassy Turkey (@USEmbassyTurkey) December 20, 2016
In a separate incident, a man with a shotgun was arrested near the U.S. Embassy in Ankara.
How other embassies responded
The man with the gun fired into the air eight times. No one was hurt, but an embassy spokesperson said the building would be closed Tuesday.
The Iranian Embassy was also closed. Russia beefed up security outside its embassy, and deputy foreign minister Oleg Syromolotov warned Russians against traveling to Turkey.
Turkey and Russia have shown the world what they can achieve when they cooperate.
The presidents of Russia and Turkey, Vladimir Putin and Recep Tayyip Erdogan, agreed that the killing of the Russian ambassador "makes us more decisive in fighting terrorism and makes today's meeting even more important," Russian Foreign Minister Sergey Lavrov said.
'Do not forget Aleppo!'
Authorities are trying to determine whether Altintas, a Turkish policeman, acted alone or if his assault was an organized terror attack, Turkey's Hurriyet newspaper reported.
His actions appeared to be well-planned. Altintas had taken leave from work on medical grounds and booked himself into a hotel near the exhibition center, Hurriyet said. A motive has not been officially determined, but Altintas yelled " Do not forget Aleppo!" after killing Karlov.
Karlov often traveled around Ankara without police escorts, which local officials said was unusual, The Washington Post reports.
These photos of Altintas, captured by AP photographer Burhan Ozbilici, show the chilling moments immediately after the shooting.
GRAPHIC VIDEO | Here's the moment of the shooting, captured on video.
The Associated Press contributed to this report.