By Adrian Croft
BRUSSELS (Reuters) - NATO is sending part of its naval rapid reaction force to the Baltic Sea as part of a drive to step up the defense of eastern European allies in response to the crisis in Ukraine, the military alliance said on Thursday.
Separately, Canada said it had offered six CF-18 fighter planes as its contribution to NATO efforts to beef up its presence in eastern Europe and reassure nervous allies there that NATO would protect them in the event of any Russian aggression.
The Pentagon said it would extend its own deployment of F-16 fighter jets to Poland through the end of the year, and encouraged other NATO allies to contribute to the detachment.
NATO, the 28-member alliance dominated by the United States, has made clear it does not plan to get involved militarily in Ukraine, which is not a NATO member.
But it announced plans on Wednesday to send more ships, planes and troops to eastern Europe to reassure members of the alliance, particularly the ex-Soviet republics in the Baltics, that are worried by Russia's annexation of Ukraine's Crimea region.
NATO gave only a broad outline of its plans on Wednesday, but some details began to emerge on Thursday.
A multinational group of five small ships - four minesweepers and a support vessel - will be sent to the Baltic Sea soon and will stay "for the foreseeable future", a spokesman for NATO's Maritime Command said.
The ships from Norway, the Netherlands, Belgium and Estonia make up one of four NATO naval groups that the alliance has available as an immediate reaction force.
The NATO "mine counter measures" group had been inactive since January but was called back to duty last week by U.S. Air Force General Philip Breedlove, NATO's top military commander.
"During this period of tension, we felt it appropriate to deploy (the group) to the Baltic Sea as part of a broad package of actions by NATO's maritime, air, and ground forces," Breedlove said in a statement.
The ships, now assembling in the German port of Kiel, will visit Baltic ports and take part in a previously scheduled exercise next month to hunt for mines and torpedoes from both world wars.
Canadian Prime Minister Stephen Harper said his country was offering six Royal Canadian Air Force CF-18 fighter aircraft to the NATO effort and up to 20 staff officers to assist with alliance planning.
"Canada continues to strongly condemn Russia's illegal occupation of Ukraine and its ongoing aggressive military provocation. Along with our NATO allies, we recognize the need to enhance security and stability in Central and Eastern Europe," Harper said in a statement.
NATO has already said it will triple its usual number of fighter jets patrolling over the Baltics from next month as part of steps to beef up its eastern European defenses.
The United States, Britain, Denmark, France and Germany are among NATO allies that have promised extra fighters to patrol the skies over the Baltic countries - which do not have fighters of their own - or elsewhere in eastern Europe.
Various allies have also offered extra ships, refueling planes and AWACS reconnaissance aircraft to the NATO effort.
At the Pentagon, U.S. Defense Secretary Chuck Hagel said he would extend the deployment to Poland of 12 F-16 fighter jets and support personnel until the end of 2014.
"The United States is also encouraging other NATO allies to contribute to the detachment," Hagel said, standing alongside his Polish counterpart. He pointed to Romania, saying it was the latest NATO member to acquire F-16s.
NATO plans to boost its defenses through a series of temporary deployments of military forces and exercises but has so far shied away from setting up new permanent bases in the east as Poland wanted.
Russia says deployment of significant NATO forces in eastern Europe, close to Russia, would violate the 1997 Founding Act, a cooperation agreement between Moscow and the alliance.
(Additional reporting by Randall Palmer in Ottawa and Phil Stewart in Washington; Editing by Hugh Lawson and Gunna Dickson)