Six Russian fighter jets were intercepted by American and Canadian planes off the coast of Alaska on Wednesday, US defence officials have confirmed.
They entered what is known as the Air Defence Identification Zone (ADIZ), but did not enter US air space.
The planes, two of which were MiG 31 jets, left the area without incident.
Officials said this type of incident was not uncommon, and happens up to 10 times a year.
The ADIZ is a zone of airspace which extends out approximately 200 miles from the coastline and is mainly within international airspace.
US sovereign air space extends 12 nautical miles from land.
Two Alaskan-based F-22 fighter jets and two Canadian CF-18 fighter jets were scrambled to intercept the Russian planes in two separate incidents on Wednesday evening and Thursday morning.
Also on Wednesday, the Swedish Foreign Ministry said two Russian military aircraft had crossed into Swedish air space south of the Baltic Sea island of Oland.
The ministry called it a "serious violation".
Sweden has said it has summoned the Russian ambassador over the incident.