Two Russian military aircraft believed to be Tu-95 bombers violated South Korea’s air defense zone on Friday, entering and leaving the area four times while South Korean ground controllers and intercept fighters warned them away.

Yonhap News relayed a report from the Joint Chiefs of Staff in Seoul:

The JCS said that the aircraft first entered the KADIZ north of the eastern island of Ulleungdo at 2:08 p.m. and flew out of it 74 kilometers southeast of Pohang at 2:35 p.m. They re-entered the KADIZ at 3:21 p.m. from the east and then left from the northwest of Jeju Island at 3:45 p.m.

At 4:08 p.m., the planes entered the KADIZ northwest of Jeju and flew out of it at 4:32 p.m. At 5:36, they re-entered the KADIZ from the east of the Dokdo islets and left at 5:53 p.m.

South Korea deployed its aircraft to send warnings to the planes, the JCS explained.

“Our military dispatched fighter jets for conducting normal tactical measures such as staging maneuvers in response and communicating warnings from the Russian military planes’ entry into the KADIZ until their exit,” the JCS said in a text message sent to reporters.

Russian aircraft have entered the KADIZ several times this year, but it is the first time that they have breached it four times in a day, a JCS official said on condition of anonymity.

The Tu-95 “Bear” bomber is a huge, ancient Cold War design that is still considered one of the most reliable workhorses of the Russian air force. Despite its ungainly appearance, it is capable of flying at high speeds and carrying an enormous payload of bombs, including cruise missiles and nuclear weapons.

In the modern era, Russia often uses the Bear to test the air defenses of other nations by doing exactly what the two planes did to South Korea on Friday, although this particular mission was more aggressive than most. Tu-95 bombers with fighter escorts briefly entered South Korea’s air defense zone in August 2017, during what now appears to have been the final iteration of the joint U.S.-South Korean Ulchi Freedom Guardian exercise.

Tu-95s actually saw combat for the first time in 2015 when they were employed to launch cruise missiles at rebel positions in Syria. The missiles deployed in Syria were capable of carrying nuclear warheads.