VILNIUS (Reuters) - NATO should upgrade its air patrols in the Baltic states into a combat-ready force that would be able to defend them in time of war, the defense alliance’s top commander said on Tuesday.

U.S. Air Force Gen. Philip Breedlove, commander of the U.S. European Command and Supreme Allied Commander for Europe, testifies before a Senate Armed Services Committee hearing on Capitol Hill in Washington, April 30, 2015. REUTERS/Jonathan Ernst

A multi-national NATO force currently has eight jets patrolling the skies over Estonia, Latvia and Lithuania. This air policing operation was increased from four jets in 2014 after Russia annexed Ukraine’s Crimean Peninsula.

“I think that the alliance does need to be ready for the air defense mission, and of course we as military men and women are looking at that capability,” Philip Breedlove, outgoing NATO Supreme Allied Commander Europe, told reporters in Vilnius.

“Air policing and air defense are meant for two different situations. The Baltic air policing is a peacetime mission”, he added.

A total force of about 600 U.S. troops has been present in the Baltic countries and Poland since April 2014, augmented by occasional rotations of other NATO allies.

U.S. President Barack Obama, in a speech delivered in Estonia in 2014, said NATO would help to safeguard the independence of the three Baltic states, which broke away from Moscow’s orbit in 1990-91 as the Soviet Union was collapsing.

Now, backed by an increase in U.S. military spending, NATO is planning its biggest build-up in eastern Europe since the Cold War to counter what the alliance, and in particular the Balts and Poland, consider to be a more aggressive Russia.

The three Baltic states, which joined both NATO and the European Union in 2004, have asked NATO for a permanent presence of battalion-sized deployments of allied troops in each of their territories. A NATO battalion typically consists of 300 to 800 troops.

“We no longer want multi-national forces to be present only as a measure of assurance or for political visibility. We want forces of deterrence, with a clear understanding that they would engage in case of a conventional attack,” Lithuania’s chief of defense Jonas Zukas told reporters.

“The air defense problem is real,” he added. “It is obvious that in case of a military conflict (in the Baltics) neither four nor eight jets would be enough.”

Moscow denies any intention to attack the Baltic states. It says Crimea is historically Russian land and that it acted legitimately in 2014 to safeguard its interests after mass street protests forced Ukraine’s then-president, the pro-Moscow Viktor Yanukovich, to flee Kiev into Russian exile.

Russia also denies arming pro-Moscow separatists battling Kiev’s forces in eastern Ukraine.