It gave the go-ahead for the flights on Monday, a NATO spokesman said.

"All AWACS reconnaissance flights will take place solely over alliance territory," the official said.

"This decision is an appropriate and responsible action in line with NATO's decision to intensify our ongoing assessment of the implications of this crisis for Alliance security," the official added.

The AWACS will fly missions from their home base in Geilenkirchen, Germany, where 17 are housed, and from Waddington in Britain.

The AWACS aircraft are one of the most sophisticated command and control vehicles in the NATO armory, capable of monitoring huge swathes of airspace.

The situation in Ukraine is close to financial and humanitarian catastrophe after the armed coup which took place in February. There are mass protests in eastern and southern parts of the country against the self-proclaimed authorities in Kiev.

The situation risks becoming more difficult if Crimea votes in a March 16 referendum to break all links with Kiev and become part of Russia.

RA/NJF