Turkish authorities have detained seven people after the assassination of the Russian ambassador to Turkey, while Russia is sending more than a dozen investigators to join the inquiry.
Andrey Karlov, 62, died from bullet wounds after a 22-year-old off-duty Turkish policeman shot him in the back as he gave a speech at an Ankara art gallery on Monday night.
"The group will act in Turkey within the framework of the investigation into the murder," Dmitry Peskov, Kremlin spokesperson, said on Tuesday.
"Eighteen people will work in the group."
READ MORE: Russian ambassador Andrey Karlov shot dead in Ankara
Peskov said Russian President Vladimir Putin and Recep Tayyip Erdogan, his Turkish counterpart, had agreed on the decision in a phone call.
Karlov was several minutes into a speech at an embassy-sponsored photography exhibition when a man who stood directly behind him in a dark suit shot him multiple times in the back from close range.
Shouting angrily while pacing around Karlov's body in front of a shocked crowd, the assailant - identified as Mevlut Mert Altintas - highlighted the situation in Aleppo and said all those responsible for what has happened there would be held accountable.
Police later killed Altintas in a exchange that lasted 15 minutes.
A three-way meeting between the foreign ministers of Turkey, Russia, and Iran in Moscow over the Syria crisis began on Tuesday where Sergey Lavrov, Russia's representative said "no quarter should be given to terrorists in Syria" after Monday's assassination.
Earlier, Putin declared, "We have to know who directed the hand of the killer".
The state-run Anadolu news agency said the attacker's mother, father, sister and three other relatives were held in the western province of Aydin, while his flatmate in Ankara was also detained.
READ MORE: Burhan Ozbilici captures Andrey Karlov's final moments
After the initial shot, the attacker approached Karlov as he lay on the ground and shot him at least one more time at close range, an AP photographer said at the scene.
Karlov's assassination has reinforced the sense of unease over the region's conflicts as also shifting alliances and relationships.
|Altintas referenced the situation in Aleppo after he shot Karlov in Ankara [Burhan Ozbilici/AP]
"On behalf of my country and my people I once again extend my condolences to Russian President Vladimir Putin and the friendly Russian people," said Erdogan.
Putin promised a response to the assassination.
"The crime that has been committed is undoubtedly a provocation aimed at derailing the ties between Russia and Turkey, as well as the peace process in Syria," said Putin from Moscow.
OPINION: The implications of Andrey Karlov assassination
"There is only one possible response to this - the strengthening of the fight against terror, and the bandits will feel it themselves."
Relations between Russia and Turkey were badly strained by the downing of a Russian fighter jet at the Syrian border in November 2015.
However, Turkey's apology earlier this year helped to overcome the rift.
READ MORE: Ankara focuses on Gulen links in Karlov assassination
"The Russians and the Turks have been trying mend the strained relations over the last few months, hoping that strong relations between the two countries would pave the way for comprehensive regional agreement on different issues, particularly on the issue of Syria," Al Jazeera's Hashem Ahelbarra, reporting from Ankara, said.
"At this particular moment, the two countries are hoping to put the peace process on track between Syrian rebels and the government," he said.
"There were huge concerns that the attack would undermine or at least erode the efforts. But officials from both governments are doing their best to contain the fallout from this assassination."
Source: Al Jazeera and news agencies