Six Russian jets were spotted flying near U.S. airspace on two separate occasions this week, according to the North American Aerospace Defence Command, or Norad.

The first group of Russian jets was detected Tuesday, with four aircraft operating in Alaska’s Air Defence Identification Zone (ADIZ), according to a Norad press release. Two days later, Norad confirmed that two more Russian aircraft were spotted flying in Alaska’s ADIZ by Norad.

“The Russian aircraft remained in international airspace and did not enter American or Canadian sovereign airspace,” Norad said in its second press release. “This Russian activity in the Alaska ADIZ occurs regularly and is not seen as a threat.”

ADIZ refers to an international airspace that’s monitored by Norad. According to the organization, it employs a layered defence network of “satellites, ground-based and airborne radars and fighter aircraft” to detect and track potential threats.

Russia confirmed that two of its Tu-95MC strategic bombers flew over waters near the U.S. The Tu-95s, known as Bears by NATO, flew over the Bering and Chukchi Seas, Russia’s defence ministry said.

“The flight was carried out in strict accordance with international rules for the use of airspace,” said Lieutenant General Sergei Kobylash, Commander of Russian long–range aviation.

The Bears are Russia’s answer to the American B-52, which has been operated by the U.S. Air Force since the beginning of the Cold War. In 2007, Russian President Vladimir Putin brought back the Soviet-era practice of sending strategic bombers on regular patrols beyond their borders.