Russia is advising all Russians currently living in or visiting Turkey to return home, and has advised against any travel to Turkey. A statement from the Russian foreign ministry Thursday said that ongoing terrorist threats in the country mean Russians visiting for personal reasons are taking an unnecessary risk.

The news comes amid heightened tensions between the two nations after Turkey shot down a Russian fighter jet  when it ventured into Turkish airspace near the Syrian border Tuesday. Turkey has refused to apologize for shooting the jet down, saying Russia is at fault for violating Turkish sovereignty and being overly aggressive. Russia, meanwhile, says that the Turkish attack was a deliberate provocation.

“I think if there is a party that needs to apologize, it is not us," Turkish President Recep Tayyip Erdogan told CNN . "Those who violated our airspace are the ones who need to apologize. Our pilots and our armed forces, they simply fulfilled their duties, which consisted of responding to ... violations of the rules of engagement. I think this is the essence."

Turkey’s downing of the Russian aircraft highlights just how fraught the Syrian civil war has become. Major world powers, including the United States and France, are conducting airstrikes against various targets in the country. The United States and other NATO members, including Turkey, have promised to defend member countries against foreign attacks as if those attacks were made on their home soil. Russia is not a member of that alliance.

Russia recently stepped up its military presence in and around the Middle East, also announcing it would install missile defense systems along the Syrian border in Latakia. Those systems have a range of about 150 miles. The Turkish border is nearby, just under 50 miles away. Russian forces have also been carrying out airstrikes in Syria in recent months, a move that is widely seen in the Western world as an attempt to prop up Syrian President Bashar Assad’s regime, which the United States and others have said needs to be replaced.