Two Russian bombers have flown within 50 miles of the California coast, prompting the US to send fighter jets to make visual contact with the aircraft.

The incident began when four TU-95 Bear H Russian Long Range Strategic Bombers and an accompanying refuelling tanker entered the so-called Air Defense Identification Zone (ADIZ) within 200 miles of the Alaska coast, the North American Aerospace Defense Command (NORAD) said.

They left the ADIZ heading west after two F-22 fighters from the Alaskan NORAD region made visual contact with them.

Five hours later, two of the Russian bombers were detected off the California coast, Major Beth Smith said.

They were visually identified by two F-15 fighters from the Continental NORAD region.

The Russian aircraft never entered US airspace during what appeared to be a routine training mission.

The incident took place on Monday, but it has only just been reported.

As part of its mission, NORAD - a joint Canada-US force - tracks and identifies all aircraft flying in the identification zone before they enter sovereign airspace, which extends 12 miles from the coastline.

Relations between the US and Russia have been poor since Moscow's annexation of Ukraine's Crimea region and pro-Russian separatists attempts to achieve autonomy elsewhere in the country.

NATO fighters protecting the Baltic states - Estonia, Lithuania, and Latvia - were also scrambled on Thursday as Russian aircraft passed near Latvian airspace on several occasions.

The military alliance has been carrying out military drills in the region since the Ukrainian crisis developed and Russia responded on Friday by training its forces to set surface-to-air missiles in the Kaliningrad exclave to ready-to-fire positions.