“Today, an aerial vehicle of unknown nationality was detected inside our airspace on the Syrian border, and when it continued its movement despite being warned three times, our aircraft on patrol mission on the border fired and shot down the vehicle within the rules of engagement,” the statement posted on the Turkish General Staff’s official website read.

“The Turkish Armed Forces is executing its tasks with determination within the rules of engagement,” the military added in the statement.

The drone fell on Turkish soil three kilometers from the border and was seized by military officers.

A U.S. official told Reuters that Washington believed the drone was of Russian origin.

The Russian Defense Ministry, however, said all of its planes in Syria had safely returned to base and that all its drones were operating “as planned.”

Russia has been conducting air operations in Syria against what it calls “terrorist groups.” Although Russia says the Islamic State of Iraq and the Levant (ISIL) is being targeted in the strikes, Turkey and its Western allies argue that the main target of the strikes is rebels fighting the Bashar al-Assad government in the war-torn country.

The incursions of two Russian fighters into Turkish airspace on Oct. 3 and 4 has brought the Syria conflict right up to NATO’s borders, testing the alliance’s ability to deter a newly assertive Russia without seeking direct confrontation.

“NATO is ready and able to defend all allies, including Turkey, against any threats,”NATO chief Jens Stoltenberg said Oct. 8.

“NATO has already responded by increasing our capacity, our ability, our preparedness to deploy forces including to the south, including in Turkey,” he said, noting that Russia’s air and cruise missile strikes were “reasons for concern.”

Turkey has previously downed a Syrian jet, a helicopter and a drone for violating its airspace.

The country adopted strict rules of engagement in 2012, after one of its F4 jet fighters was downed by Syria.

Turkey later announced that any naval, air or land force vehicle approaching Turkish territory from Syria would be considered a threat.

The Turkish Air Force shot down a Syrian helicopter at the border on Sept. 16, 2013, after it reportedly violated Turkey’s airspace.

On March 23, 2014, a Syrian jet was downed by Turkish fighter jets after it crossed into Turkish airspace a week before local elections.

Finally, on May 16, 2015, Turkey downed a Syrian surveillance drone after it violated Turkish airspace.