"NORAD detected, tracked, and intercepted two Russian TU-95 and two PRC H-6 military aircraft operating in the Alaska Air Defense Identification Zone," it said.

The zone is a perimeter in which air traffic is monitored beyond the border of national airspace to provide additional reaction time in case of hostile actions.

Intercepts of Russian aircraft -- in which they are contacted visually or electronically by US or Canadian planes -- are relatively common in the area.

"Fighter jets from the United States and Canada conducted the intercept," NORAD said, adding that the bombers "remained in international airspace and did not enter American or Canadian sovereign airspace," and that their activity "is not seen as a threat."