(CNN) Russia warned it will not make "concessions to terrorists" a day after its ambassador was gunned down in the Turkish capital, Ankara.

Russian Foreign Minister Sergey Lavrov said his country remained "determined to fight terrorism" after a meeting Tuesday in Moscow with his Turkish and Iranian counterparts.

Tuesday's meeting had been arranged to discuss the situation in the Syrian city of Aleppo before Russian ambassador Andrey Karlov was gunned down Monday at the opening of an art exhibition in Ankara. It comes as an 18-strong investigative team of Russia's special agencies arrived in Turkey to help authorities with their inquiries.

Turkey's official Anadolu news agency reported that the gunman had been neutralized. But it was not immediately clear whether the attacker was killed or captured by police. Later, Turkey's Interior Ministry said Altintas had been killed.

The gunman stands near the body of Karlov. "Only death will remove me from here. Everyone who has taken part in this oppression will one by one pay for it," he said in the video.

The gunman stands near the body of Karlov. "Only death will remove me from here. Everyone who has taken part in this oppression will one by one pay for it," he said in the video.

People cower after Karlov was shot. "Get back! Get back!" the gunman could be heard shouting in Turkish.

People cower after Karlov was shot. "Get back! Get back!" the gunman could be heard shouting in Turkish.

The gunman gestures near the body of Karlov. In a video circulating on social media, the shooter is heard shouting, "Allahu akbar (God is greatest). Do not forget Aleppo! Do not forget Syria! Do not forget Aleppo! Do not forget Syria!" Russia has been instrumental in helping Syrian President Bashar al-Assad's regime in its push to retake the eastern sector of Aleppo, which had been held by rebels for nearly four years. Russia is also the most powerful ally of Assad's regime and has carried out airstrikes since September 2015 to prop up the embattled leader.

The gunman gestures near the body of Karlov. In a video circulating on social media, the shooter is heard shouting, "Allahu akbar (God is greatest). Do not forget Aleppo! Do not forget Syria! Do not forget Aleppo! Do not forget Syria!" Russia has been instrumental in helping Syrian President Bashar al-Assad's regime in its push to retake the eastern sector of Aleppo, which had been held by rebels for nearly four years. Russia is also the most powerful ally of Assad's regime and has carried out airstrikes since September 2015 to prop up the embattled leader.

Karlov's body lies on the floor as the gunman stands nearby.

Karlov's body lies on the floor as the gunman stands nearby.

The man holds his gun up after shooting Karlov. The attack occurred at the Cagdas Sanat Merkezi modern arts center in Ankara. Turkish Interior Minister Suleyman Soylu said in a news conference that the gunman was Mevlut Mert Altintas, a Turkish police officer.

The man holds his gun up after shooting Karlov. The attack occurred at the Cagdas Sanat Merkezi modern arts center in Ankara. Turkish Interior Minister Suleyman Soylu said in a news conference that the gunman was Mevlut Mert Altintas, a Turkish police officer.

Andrey Karlov, the Russian ambassador to Turkey, speaks at the opening ceremony of a photo exhibit in Ankara, Turkey, on Monday, December 19. Moments later, he was fatally shot. Associated Press photographer Burhan Ozbilici was at the event and watched the assassination unfold.

Andrey Karlov, the Russian ambassador to Turkey, speaks at the opening ceremony of a photo exhibit in Ankara, Turkey, on Monday, December 19. Moments later, he was fatally shot. Associated Press photographer Burhan Ozbilici was at the event and watched the assassination unfold.

Envoy's body returned to Moscow

Marina Davydova Karlova bids farewell Tuesday to her husband, the late Russian envoy, in Ankara.

Karlov's body arrived in Moscow late Tuesday. The ambassador was bestowed honors upon arrival in a ceremony attended by Lavrov, Turkish Foreign Minister Mevlut Cavusoglu and the widow of the deceased, according to Russia's Foreign Ministry.

Earlier Tuesday, Lavrov said the tragedy made the talks even more urgent, according to Russian state-run news agency Sputnik.

"This tragedy makes all of us more determined to fight terrorism," Lavrov was quoted as saying.

He hoped the talks would "create conditions for a more efficient delivery of humanitarian aid without making any concessions to terrorists," he said.

"It is necessary to establish all the circumstances of the organization and (the) execution of the terrorist act as soon as possible."

Just paid our respects to our Russian colleague Andrei Karlov at airport. Sad day. Never want to do this again. pic.twitter.com/3RYcUeklAn — Richard Moore (@UKAmbRichard) December 20, 2016

Cavusoglu said the attack was intended to "harm our relations and destroy all the achievements we have made together recently."

He welcomed the investigative team from Russia, saying the two countries would work together to "uncover who is behind this vile and treacherous terror attack."

"Turkey and Russia have recently proven what they can achieve when they cooperate, not only to their own people but to the whole world," he said.

"We will maintain this cooperation in Syria in order to reach a political resolution and also extend the cooperation to other areas."

He announced the street that houses the Russian Embassy in Ankara will be renamed in Karlov's honor.

Turkish soldiers stand near the coffin of the Russian ambassador Tuesday at the Ankara airport.

Shooter's relatives taken in for questioning

On Monday night, Altintas, the police officer, fired several shots at Karlov , shouting, "Allahu akbar (God is greatest). Do not forget Aleppo! Do not forget Syria! Do not forget Aleppo! Do not forget Syria!"

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Video and photographs taken during the exhibition show that shortly before the shooting, Altintas had been standing behind Karlov while the envoy was making remarks. Turkish security forces eventually killed Altintas, Turkey's Interior Ministry said.

Seven people were taken in for questioning in relation to the shooting, including the shooter's parents, sister, uncle and two other relatives. A roommate, a police officer, was also arrested, according to Turkish state news agency Anadolu.

Altintas' uncle was released under "judicial control," or bail-like conditions, Anadolu quoted security sources as saying.

whose movement Turkey considers a terrorist group. The school was shut down after a According to Anadolu, the uncle was a former senior executive at a private school connected to cleric Fethullah Gulen whose movement Turkey considers a terrorist group. The school was shut down after a failed coup in July.

Emergency vehicles respond to the shooting of the Russian ambassador in Ankara.

Anadolu also reported that books about al Qaeda and Gulen's movement, which the Turkish government calls the Fethullah Gulen Terrorist Organization, were found after a search of Altintas' home.

Turkey alleges that members of Gulen's movement were behind the coup attempt.

The failed coup triggered a wave of arrests, detentions and dismissals of those suspected of any involvement.

The rest of Altintas' relatives were taken in for questioning, the agency quoted security sources as saying.

The ambassador's assassination came at a time of thawing relations between Russia and Turkey and at a pivotal moment in Syria in which Russia has been instrumental in President Bashar al-Assad's push to retake rebel-held areas.

Putin: Shooting a 'provocation'

Russian President Vladimir Putin said the killing was a clear provocation aimed at undermining not just the normalization of Russian-Turkish relations but also the "peace process in Syria" promoted by Russia, Turkey, Iran and other countries.

"The only response we should offer to this murder is stepping up our fight against terror, and the criminals will feel the heat," Putin said in televised remarks.

Turkish President Recep Tayyip Erdogan echoed Putin's sentiments, saying "the Russian government and the Turkish republic have the will to not fall into that provocation."

Putin will delay his annual news conference on Thursday in order to pay his respects to the slain ambassador, whose funeral will be held that day, Sputnik reported.

Roles of Russia and Turkey in Syria

Human rights groups and other countries have denounced Russia over its backing of the Syrian leader.

Moscow, the most powerful ally of the Assad regime, has carried out airstrikes since September 2015 to prop up the embattled ruler. As one of the five permanent members of the UN Security Council, Russia has used its veto powers to block a political solution to end the war.

The bombardment in Syria has drawn criticism from Western powers, with President Barack Obama on Friday accusing Russia of slaughtering civilians in the besieged city of Aleppo in concert with the Assad regime. Moscow has recently tried to distance itself from the assault in eastern Aleppo.

Turkey's involvement in Syria is complicated. On one hand, the Turks are eager to help eradicate ISIS. On the other, Ankara has worked to drive Kurdish fighters from the Syrian side of the border.

Meanwhile, the United States supports Kurdish groups in both Syria and Iraq as critical partners in the battle against ISIS.

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Embassies closed

All US embassy and consulates in Turkey were to be closed Tuesday after a separate incident, hours after the Russian envoy's assassination.

Turkish police arrested a man who fired into the air with a shotgun outside the US Embassy in Ankara, Anadolu reported.

Video fed by Turkish video news agency IHA showed security officers leading a handcuffed man into an unmarked police car as he shouted in Turkish, "I swear to God. Don't play with us." No one was injured.