Published October 30, 2014

Greece's Prime Minister Antonis Samaras, left, shakes hands with NATO Secretary General Jens Stoltenberg before their meeting at Maximos Mansion in Athens, Thursday, Oct. 30, 2014. Stoltenberg said the alliance is increasing its readiness and air policing following a spike in airforce activity in eastern Europe by Russia, which he urged to end destabilizing actions in Ukraine. (AP Photo/Eurokinissi, Tatiana Bolaris) GREECE OUT(The Associated Press)

Members of Greek Navy special forces operate during a Greek joint military exercise ''Pyrpolitis'' at the Saronic Gulf, south of Athens on Thursday, Oct. 30, 2014. NATO Secretary General Jens Stoltenberg attended the drill as he is in Athens for talks expected to focus on efforts to counter Islamic State militants in Iraq, the ongoing crisis in Ukraine and renewed tension between Greece and Turkey over oil-and-gas exploration off the coast of divided Cyprus. (AP Photo/Thanassis Stavrakis)(The Associated Press)

Members of Greek Navy special forces operate from a military helicopter during a Greek joint military exercise ''Pyrpolitis'' at the Saronic Gulf, south of Athens on Thursday, Oct. 30, 2014. NATO Secretary General Jens Stoltenberg attended the drill as he is in Athens for talks expected to focus on efforts to counter Islamic State militants in Iraq, the ongoing crisis in Ukraine and renewed tension between Greece and Turkey over oil-and-gas exploration off the coast of divided Cyprus. (AP Photo/Thanassis Stavrakis)(The Associated Press)

Military helicopters operate during a Greek joint military exercise ''Pyrpolitis'' at the Saronic Gulf, south of Athens on Thursday, Oct. 30, 2014. NATO Secretary General Jens Stoltenberg attended the drill as he is in Athens for talks expected to focus on efforts to counter Islamic State militants in Iraq, the ongoing crisis in Ukraine and renewed tension between Greece and Turkey over oil-and-gas exploration off the coast of divided Cyprus. (AP Photo/Thanassis Stavrakis)(The Associated Press)

A Greek Navy officer gives directions to a helicopter during a Greek joint military exercise ''Pyrpolitis'' at the Saronic Gulf, south of Athens on Thursday, Oct. 30, 2014. NATO Secretary General Jens Stoltenberg attended the drill as he is in Athens for talks expected to focus on efforts to counter Islamic State militants in Iraq, the ongoing crisis in Ukraine and renewed tension between Greece and Turkey over oil-and-gas exploration off the coast of divided Cyprus. (AP Photo/Thanassis Stavrakis)(The Associated Press)

ATHENS, Greece NATO's new chief says the alliance is increasing its readiness and air policing following a spike in Russian air force activity in Eastern Europe.

Jens Stoltenberg says while NATO is not back on Cold War terms with its former arch-enemy, recent Russian behavior has severely undermined the trust built up over decades.

Tensions have been running high between NATO and Russia since Russia annexed the Crimean Peninsula from Ukraine in March.

Speaking Thursday during a visit to Athens, Stoltenberg said the trans-Atlantic military alliance "remains vigilant" in view of this year's tripling of Russian military flights along NATO's eastern borders.

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NATO chief: Russia has tripled military flights along NATO's eastern borders this year