Poland hailed the deployment of a Patriot battery and troops on its soil on Wednesday as an important boost for its national security, but Russia said the move harmed regional 'trust and predictability.'

The surface-to-air missile battery, which is accompanied by 100 US military personnel, arrived Sunday at Morag in northern Poland's picturesque Mazurian lake district, about 70 km from Russia's Baltic exclave of Kaliningrad.

Its mission is to train Polish troops and it poses no threat to Russia's vast military arsenal, but its presence is hugely symbolic for Poland, which has long complained it hosts no major Nato hardware or troops 11 years after joining the alliance.

'We in Poland see the deployment of the Patriot battery here as a move toward strengthening our national security and ties with America,' Defence Minister Bogdan Klich told a welcoming ceremony also attended by U.S. Ambassador Lee Feinstein.

Under a 2008 accord between Warsaw and Washington, the battery, which is normally stationed in Germany, will be deployed in Poland for about one month four times a year. The first deployment ends on June 16.

Warsaw expects to have a Patriot battery permanently stationed on its territory from 2012. US officials said there were no plans to arm the battery.

'It's a purely defensive system, entirely for training. We don't have any missiles here (in Morag) nor will we ever have,' said Lieutenant Daniel Herrigstad, public affairs officer for the U.S. army in Europe, adding that Morag -- home to a Polish mechanised battalion -- lacked storage facilities for missiles.

The Patriot battery deployment is not linked to ongoing U.S. talks with Poland and other ex-communist states about future missile defense systems that Moscow strongly opposes.

For Poland, the battery provides belated US recognition of its loyalty as an ally which sent troops to Kosovo and Iraq and currently has about 2,600 troops serving in Afghanistan.

But Russia, Poland's communist-era overlord, reiterated its criticism of the Patriot deployment on Wednesday.

'Such military activity does not help to strengthen our mutual security, to develop relations of trust and predictability in this region,' a Russian Foreign Ministry spokesman said Wednesday.

'We have repeatedly stated that we do not understand the logic and sense of cooperation between the United States and Poland in this sphere,' Russia's Foreign Ministry said.

'We note with regret that our questions to the Polish and U.S. sides have remained unanswered, as well as our arguments in favor of temporarily moving the deployment region as far as possible from Russian borders.'

The Patriot's arrival coincides with fresh efforts by Moscow and Warsaw to improve bilateral ties, long strained by rows over missile defense, Nato enlargement, energy supplies and history.

Russia has shown particular sensitivity to Polish concerns since a plane crash on its territory last month killed Poland's President Lech Kaczynski and 95 others, mostly senior officials.

There was no immediate hint of any retaliatory Russian move to the Patriot deployment in the Foreign Ministry statement.

Russia's defense ministry denied in January suggestions it might boost its Baltic naval fleet in response to the Patriot deployment in Poland.

Moscow relies heavily on its strategic nuclear missiles for defense because of the poor state of its conventional troops, so it is particularly sensitive to any deployments of anti-missile systems such as the Patriot.-Reuters