Speaking to reporters in Istanbul, Erdogan said another Russian warplane violated its airspace Friday despite repeated warnings in multiple languages. The incursion comes two months after NATO-member Turkey’s military shot down a Russian jet for crossing over its territory.

“We regard this infringement which came despite all our warnings in Russian and in English as an effort by Russia to escalate the crisis in the region,” Erdogan said. “If Russia continues the violations of Turkey’s sovereign rights, it will be forced to endure the consequences.”

He did not specify what those consequences might be.

Russia`s Defense Ministry denied the accusations. "There have been no violations of Turkey’s airspace by aircraft of the Russian air group in the Syrian Arab Republic," the ministry said, according to TASS news agency.

Defense Ministry spokesman Maj. Gen. Igor Konashenkov called the allegations "unsubstantiated propaganda" by Turkey.

Erdogan said he attempted to reach Russian President Vladimir Putin to discuss the issue but that the Russian leader did not respond.

“These irresponsible steps do not help the Russian Federation, NATO-Russia relations or regional and global peace,” Erdogan said. “On the contrary they are detrimental.”

Turkey’s Foreign Ministry said the Russian SU-34 crossed into Turkish airspace on Friday, ignoring several warnings in Russian and in English by Turkish radar units. It said Ankara summoned the Russian ambassador to the ministry Friday evening to “strongly protest” the violation. It was not clear where exactly the new infringement occurred.

NATO Secretary General Jens Stoltenberg also called on Russia “to act responsibly and to fully respect NATO airspace” but also urged “calm and de-escalation” of tensions between Moscow and Ankara.

“Russia must take all necessary measures to ensure that such violations do not happen again,” he said in a statement. “NATO stands in solidarity with Turkey and supports the territorial integrity of our ally, Turkey.”

This week, Pentagon officials met with Russian counterparts to discuss an ongoing agreement on flight safety over Syrian airspace. The two sides say the agreement is meant to avoid accidents and unintended confrontations in the close proximity of bombing raids.

That came in response to a string of Russian jets have narrowly missing coalition planes in the past. On Monday, a Russian SU-27 sped past a U.S. Air Force spy plane over the Black Sea. The Pentagon called the maneuver “unsafe and unprofessional.”

In November, Turkey shot down a Russian plane that it said violated its airspace near Syria, touching off a crisis between the two countries. It was the first time in more than half a century that a NATO nation had shot down a Russian plane.

Turkey brought down the Russian SU-24 bomber near the border with Syria on Nov. 24, saying it violated its airspace for 17 seconds despite repeated warnings. Russia insists the plane never entered Turkish airspace. One pilot and a Russian marine of the rescue party were killed in the incident.

The Russian military quickly sent missile systems to Syria and warned that it would fend off any threat to its aircraft. Moscow also punished Turkey by imposing an array of economic sanctions.

On Saturday, Stoltenberg said NATO agreed in December to increase the presence of an early warning system over Turkey to increase the country’s air defenses. He said the decision was taken before Friday’s incident.

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