Polish and US officials unveiled on Wednesday the first battery of US surface-to-air Patriot-type missiles to be stationed on Polish soil, a move that has vexed Poland's communist-era master Russia.

"We regard the deployment of the Patriot system in Poland as an important step increasing our national security and in developing strategic cooperation with the United States," said Polish Defence Minister Bogdan Klich, whose country joined NATO in 1999 a decade after the communist bloc collapsed.

Klich formally welcomed the 100-strong US unit that had arrived at a Polish army base in the northern town of Morag at the weekend, and viewed the three unarmed Patriot missile launchers which Polish troops will be trained to use.

"Your arrival here in Poland has two dimensions, political and symbolic. Politically, it's about Poland's security. And symbolically because on Polish soil, for the first time, US soldiers will be stationed long-term," he said.

The unit, normally stationed in Kaiserslautern, western Germany, is the first to take part in a 30-day training deployment in Poland.

Similar rotations are due every quarter until a year-round deployment starts in 2012.

Klich said he hoped staunch ally Washington would station more troops in Poland in the future.

The Patriot system, which the US military says has a range of "more than 100 kilometres", aims to intercept surface-to-surface missiles.

Morag is just 60 kilometres (40 miles) from the border with Russia's Kaliningrad territory.

The deployment has raised Russian hackles.

"It is unclear why such a region located in the immediate proximity to the Russian border has been found for the deployment and where, as far as we know, there are no objects of military infrastructure," the Interfax news agency quoted an unnamed Russian foreign ministry official as saying.

The official said the move would "not lead to the strengthening of stability in this region but on the contrary decrease trust and predictability".

Poland has repeatedly insisted Morag was not chosen for political or strategic reasons, but simply due to infrastructure.

The US unit's spokesman, Lt. Col. Daniel Herrigstad, underlined that. He said Morag's railhead and secure storage were the primary reason, and sites elsewhere in Poland could also be used in the future.

Klich rejected suggestions the deployment was a threat.

"You don't need to be a specialist to realise that this system can't be changed from defensive to offensive. Hence this system doesn't pose a risk to anyone, to none of our neighbours," he told reporters after the ceremony.

"We will be repeating that every day if we have to," he said.

"We don't treat Russia as a country that poses a threat to our country," he added, and said the deployment was simply part of an ongoing military upgrade since Poland joined NATO.

US ambassador Lee Feinstein underscored Klich's remarks.

"Of course the Patriots are an entirely defensive weapons system that poses no threat to any country," Feinstein told reporters in Morag.

Feinstein said the battery is set to be armed after the Poles have undergone basic training, however.

"It's a concept of being able to walk before you run. So we're beginning this operation in the configuration we have today, but in the future the operation will of course include live missiles," he explained.

Warsaw and Washington struck the Patriot deal in 2008 amid related talks on a US plan to install a controversial anti-missile shield in Poland and the neighbouring Czech Republic.

In September 2009 US President Barack Obama scrapped that shield project, which had been pushed by his predecessor George W. Bush.

The shield plan had enraged Russia, which dubbed it a security menace on its doorstep, although Washington insisted the aim was to ward off a potential long-range missile threat from Iran.