Turkish police have detained six people over the killing of the Russian ambassador on Monday, state media said.
The ambassador was shot in the back as he gave a speech in Ankara by an off-duty police officer shouting "Don't forget Aleppo!" and "Allahu akbar!" as screams rang out.
A video showed the attacker pacing about and shouting as he held the gun in one hand and waved his other hand in the air.
The state-run Anadolu agency said on Tuesday that the attacker's mother, father, sister and two other relatives were held in custody in the western province of Aydin, while his flatmate in Ankara was also detained.
A Russian delegation was due to arrive in Ankara at 11 am (08.00 GMT) to conduct investigations into the attack, broadcaster CNN Turk reported.
The United States said its three missions in Turkey would be closed on Tuesday after a gun was fired in front of the US embassy in Ankara overnight.
The embassy is near the art gallery where Karlov was shot and Turkish police detained a man over the incident, state media reported.
Russia's foreign ministry said on Tuesday the two countries' foreign ministers had underlined the need to put more effort into effectively fighting terrorism in a phone call overnight.
The Russian, Turkish and Iranian foreign ministers will meet in Moscow later on Tuesday to discuss the crisis in Syria.
Security Threats
Turkey faces multiple security threats, including from the Islamic State militant group. A spokesman for the hardline Sunni Muslim group urged sympathizers around the world this month to carry out a fresh wave of attacks, singling out Turkish diplomatic, military and financial interests as preferred targets.
However, a senior Turkish security official said there were "very strong signs" the gunman belonged to the network of the US-based cleric Fethullah Gulen, who Ankara says orchestrated a failed coup in July.
Erdogan has denounced Gulen as a terrorist, but the cleric, a former ally, denies the accusation, and has also denied any role in the assassination.
Russia is an ally of Syrian President Bashar al-Assad and its air strikes helped Syrian forces defeat rebel resistance in Aleppo last week.
Turkey, which seeks Assad's ouster, has been repairing ties with Moscow after shooting down a Russian warplane over Syria last year.
