NATO said Wednesday it will keep military channels of communication with Russia open to avoid any misunderstandings over military activity, as the Ukraine crisis stokes tensions not seen since the Cold War.

The 28 member states of the US-led alliance, set up originally to protect Western Europe from the Soviet Union, "agreed that at this time of tension there is a need for continued communications among NATO and Russian military to avoid any incidents," a NATO press officer said.

"NATO military authorities should continue to keep channels of military communications open and to use them when necessary to avoid any possible misunderstandings related to military activities," he added.

In response to Russia's intervention in Ukraine and its annexation of Crimea in March, NATO suspended all cooperation with Moscow through the NATO-Russia Council, the main forum for political contacts set up in 2002 when ties were much closer.

As the crisis has deepened, NATO has stepped up readiness in response to what it sees as a more dangerous and assertive Russia.

Russia in turn has increased its military activity, launching high-profile aircraft sorties to test NATO's defences and sending navy ships around the world to reassert its status as a great power.

Some NATO allies such as Germany, with close economic and political ties to Russia, have been especially uneasy, fearing the crisis could turn into a long lasting stand-off reminiscent of the worst days of the Cold War.

German Foreign Foreign Minister Franz Walter Steinmeier said earlier that NATO foreign ministers had asked alliance head Jens Stoltenberg "to look for ways to rebuild contacts on the level of military experts".

"This is to guarantee that we have a minimum of mutual exchange with Russia in these critical times," Steinmeier said.