MOSCOW — A team of Russian detectives arrived in Turkey early Tuesday to assist with the investigation into the killing of Russia’s ambassador by a Turkish police officer, an act leaders in both countries said was an effort to rupture a rapprochement between the two regional powers as they try to reach an accommodation over Syria’s civil war.

A Kremlin spokesman said President Vladimir Putin and Turkish President Recep Tayyip Erdogan had jointly agreed to include the Russian task force in the investigation. Officer Mevlut Mert Altintas gunned down Ambassador Andrei Karlov as the diplomat spoke before an exhibition of Russian photos at an art gallery in the Turkish capital of Ankara Monday evening.

People crouch in a corner after Andrei Karlov, the Russian ambassador to Turkey, was shot at a photo gallery in Ankara, Turkey, on Monday. Turkey and Russia plan to work together to investigate the assassination. Associated Press/Burhan Ozbilici

After killing the ambassador, Altintas, a 22-year-old officer with the riot police, denounced Russia’s role in the Syrian war, screaming: “Don’t forget Aleppo! Don’t forget Syria!” He was later killed in a gun battle with the police.

The assassination, which was captured in stunning detail by an Associated Press photographer and other journalists, brought into sharp relief the violent worldwide reverberations of Syria’s bloody civil war.

The ambassador’s killing has also shocked Turkey, adding to a string of recent militant attacks and political turmoil that have hurt the economy and increasingly isolated the country.

“I believe that every person who is going to Turkey should think twice before doing so, because terror attacks have been happening there on a practically daily basis,” Russian Deputy Foreign Minister Oleg Syromolotov told reporters in Moscow.

Turkey remained on edge on Tuesday, as authorities detained relatives of Altintas and searched his family home in the Soke district, in the west of the country, Turkish media reported. In what appeared to be a separate incident, a man fired shots near the entrance of the U.S. embassy in Ankara overnight. A State Department official said that no one was hurt.

Turkey’s semi-official Anadolu News Agency said that the gunman, who was identified only as Sahin S, arrived at the embassy early Tuesday morning, and fired several shots in the air with a pump-action rifle he had hidden under his coat.

He was detained and was being questioned, the news agency said. The embassy, as well as the U.S. consulates in Istanbul and Adana were closed on Tuesday because of the shooting, according to a State Department statement.

Karlov regularly traveled around Ankara without police protection, an unusual decision given the heightened level of threat in the country since a July attempted coup and a string of terrorist attacks by militant groups, Turkish officials said.

Officials, who asked not to be named because they are not authorized to speak to the press, said their investigation was in its earliest stages but they pointed to indications that the alleged shooter may have links to a shadowy movement led by Fethullah Gulen, an exiled Turkish preacher.

Erdogan has accused the movement of mounting a failed coup in July, and since then, frequently implicated in group in various plots to destabilize Turkey.

Gulen has denied involvement in the coup, and he released a statement on Monday condemning the killing of Karlov.

Investigators said that Altintas entered a police college in 2012. He was allowed to carry a weapon into the event with Karlov because he was carrying a police identification, officials said. There was not yet any evidence to suggest that the shooter belonged to any radical Islamic groups, such as Islamic State or the Nusra Front, an Al-Qaida affiliated group, investigators said.

At the time of the shooting, the Turkish foreign minister was on a plane en route to Russia to take part in a meeting with his Iranian and Russian counterparts Tuesday, as part of the effort to halt hostilities in Syria’s civil war.

The shooting was among the most brazen retaliatory attacks yet on Russia since Moscow entered the war in Syria on the side of President Bashar Assad and unleashed a bombardment on Aleppo that has drawn international condemnation for what observers on the ground have called indiscriminate attacks on civilians.

Putin on Monday night called the shooting a “provocation aimed at rupturing ties between Russia and Turkey,” a statement later echoed by Erdogan.

Erdogan and Putin, two strongmen with global aspirations, have found common ground in recent months in their desire to secure an end to the Syrian war that would guarantee their long-term influence at a time when U.S. diplomacy has collapsed.

The newfound cooperation between Russia and Turkey over Syria was exemplified by the deal they brokered last week for the evacuation of besieged people from the last few blocks of rebel-held territory in eastern Aleppo.

The statements by Putin and Erdogan suggested that the assassination may not disrupt their budding convergence of interests. Until last summer, the two presidents had been bitter rivals over Syria, supporting opposite sides in the war and embroiled in recriminations over the shoot-down by Turkey of a Russian fighter jet in November 2015.

Those circumstances have led some Russian politicians to accuse the West of complicity in the attack.

“They are afraid of that alliance. It’s a counterweight to the European Union and NATO,” said Vladimir Zhirinovsky, a nationalist politician whose often outlandish remarks on foreign policy are sometimes seen as a trial balloon for things the Kremlin would rather not say.

Many players risk losing out in any Russian-Turkish deal over the future of Syria, including the U.S.-backed Syrian opposition, extremists with the Islamic State, and Syria’s al-Qaida affiliate.

The United States, meanwhile, joined other nations in condemning the shooting.

“Our thoughts and prayers are with his loved ones, the Russian people, and with the other victims who were injured in this shooting,” Secretary of State John F. Kerry said in a statement. “We stand ready to offer assistance to Russia and Turkey as they investigate this despicable attack, which was also an assault on the right of all diplomats to safely and securely advance and represent their nations around the world.”

Karlov started his diplomatic career in 1976 during the Soviet era and took the post in Ankara in July 2013, according to the embassy’s website. Putin referred to him as a “brilliant diplomat” who “had excellent relations with the leadership of Turkey and other political forces.”

The incident could spur even more vigorous efforts between Russia and Turkey to secure their role as Syria’s main power brokers and negotiate a settlement to the war on their terms. Aaron Stein, a resident senior fellow at the Atlantic Council’s Rafik Hariri Center for the Middle East, said that any fallout “will entirely depend on Russia’s reaction.”

“All indications thus far is that they will retain the relations they have built with Turkey since the rapprochement a couple of months ago,” he added.

The recent cease-fire cobbled together was to Russia’s long-term benefit in Syria, while also addressing Turkey’s real concern about civilian casualties, Stein said.

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