ANKARA, Turkey (AP) — Turkey shot down an unidentified drone that flew into its airspace Friday near the Syrian border, while Russian President Vladimir Putin said his country’s air campaign backing a Syrian government offensive has killed hundreds of militants.

A U.S. official said the downed drone was Russian, but Moscow staunchly rejected the claim.

The incident underlined the potential dangers of clashes involving Russian, Syrian and U.S.-led coalition planes in the increasingly crowded skies over Syria. Russian and U.S. military officials have been working on a set of rules to prevent any problems.

The Turkish military said it issued three warnings before shooting down the aircraft with its fighter jets. It didn’t specify how it had relayed the warnings to the operators of the drone.

The drone crashed 3 kilometers (about 2 miles) inside Turkish territory, said Foreign Minister Feridun Sinirlioglu. “We have not been able to establish who the drone belongs to, but we are able to work on it because it fell inside Turkish territory,” he added.

Earlier this month, Turkey had protested two incursions by Russian warplanes, which also drew strong condemnation from Turkey’s NATO allies.

The U.S., Russia and the Syrian government all operate drones in the region.

The drone was definitely not American, and the U.S. believes it was Russian, said a U.S. defense official, who was not authorized to discuss details of the incident and spoke on condition of anonymity.

Moscow strongly denied ownership of the drone.

“I state with absolute responsibility that all our drones are either performing tasks or staying at the base,” said Col.-Gen. Andrei Kartapolov, a deputy chief of the Russian General Staff, speaking at a meeting with foreign military attaches in Moscow.

The Lebanon-based pro-Syrian Al-Mayadeen TV quoted an unidentified Syrian military official as saying that no Syrian or Russian warplane or drone was shot down over Turkey.

Seeking to soothe Turkey’s anger over violation of its airspace by Russian aircraft, Moscow sent a high-level military delegation to discuss preventing such incidents.

“They apologized a few times, said it happened by accident, and that they have taken measures so that it will not occur again,” Sinirlioglu said of Thursday’s talks in Ankara with the Russian delegation.

Since 2013, Turkey has shot down a Syrian military jet, a helicopter and a surveillance drone that strayed into Turkish airspace. The incidents occurred after Ankara changed its rules of engagement following the downing of a Turkish fighter jet by Syria.

Turkey, which patrols the border with F-16s, has also reported numerous incidents of harassment by Syrian fighter planes or Syria-based surface-to-air missile systems locking radar on the aircraft.

Russia began its air campaign Sept. 30, and Syrian troops and allied militiamen launched a ground offensive in central Syria a week later. They have so far met stiff resistance from rebels using U.S.-made TOW anti-tank missiles that have impeded swift breakthroughs, although they have taken a few villages from rebels in the past week.

On Friday, Syrian troops supported by Russian air power and fighters from Iran and the Iranian-backed Hezbollah group pressed an assault against rebels in central Syria and launched another offensive in the northern province of Aleppo to try to recapture territory, according to activists and the government. The multiple-front offensives appear aimed at stretching rebel lines and keeping the insurgents off-balance.

A Syrian military spokesman said in a televised statement that the army launched an operation in the Damascus rebel-held neighborhood of Jobar as well as the suburb of Harasta. He added that troops now control of all hills that overlook Harasta and the nearby suburb of Douma, a stronghold of Islam Army rebel group.

The attack appears aimed at securing President Bashar Assad’s seat of power that has been shelled recently from rebel-held areas.

The fighting is particularly intense in the central province of Homs, where the Syrian Observatory for Human Rights said about 60 people were killed in Russian airstrikes and fighting. The Local Coordination Committees, an activist network that follows the war, put the death toll at 57.

The Russian military has rejected claims of civilian casualties, saying its planes haven’t targeted populated areas.

At a meeting in Kazakhstan of leaders of former Soviet nations, Putin said his air force has achieved “impressive” results in Syria.

“Dozens of control facilities and ammunition depots, hundreds of terrorists and a large number of weapons have been destroyed,” he said.

Putin said the Russian air campaign against the Islamic State group and other radicals in Syria will continue “for the period of the Syrian troops’ offensive operations against terrorists.” He would not elaborate.

Between 5,000 and 7,000 people from Russia and other former Soviet countries are fighting alongside Islamic State militants, he said.

“We can’t allow them to use the experience they have just gained in Syria back home,” he added.

Russian jets have flown 669 sorties since Sept. 30, including 394 this week, said Kartapolov, the Russian general.

He emphasized the urgent need for a U.S.-Russian agreement on avoiding clashes, which is being negotiated.

“The sky over Syria is swarming with aircraft,” Kartapolov said. “Such intense and uncoordinated use of air power in Syria’s relatively small airspace may sooner or later lead to an incident.”

In a bid to dispel claims by the U.S. and its allies that Moscow is focused on moderate rebels instead of its declared targets of Islamic State militants, Kartapolov said the Russian Defense Ministry would send a detailed map showing positions of the IS and Syria’s al-Qaida affiliate targeted by the Russian aircraft.

“Our aircraft have been used on targets outside of populated areas,” he said.

Kartapolov also criticized the U.S.-led coalition for striking a power plant near Aleppo, leaving the city without electricity and paralyzing its water supply and sewage system, something he said could only increase the flow of refugees.

In a separate interview with the daily newspaper Komsomolskaya Pravda, Kartapolov shrugged off the U.S. claim that four of 26 cruise missiles launched at targets in Syria by the Russian navy from the Caspian Sea had crashed in Iran.

“The Pentagon may say whatever it wants,” he said. “All our missiles reached their targets.”

Kartapolov said the Russian jets haven’t yet faced any surface-to-air missiles and warned that their use by rebels would signal a foreign involvement.

Following a similar statement by Putin, the general ruled out Russian military involvement in ground action in Syria. He said Russian air and land assets in Syria will be pulled together with its Soviet-era Tartus navy facility in one base.

Kartapolov wouldn’t offer any further details, and Putin’s spokesman, Dmitry Peskov, refused to comment on the issue.

Russian warships in the Mediterranean helped provide cover for its air base in the coastal province of Latakia and could take part in attacks on targets in Syria, Kartapolov said.

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Isachenkov reported from Moscow. AP National Security Writer Robert Burns in Washington, Zeina Karam and Bassem Mroue in Beirut contributed to this report.