Polish authorities and ordinary Poles welcomed Saturday US troops who arrived this week as part of an unprecedented deployment to NATO's eastern flank aimed at deterring Russia.

"Welcome to Poland," Prime Minister Beata Szydlo told US troops in Zagan, the Polish town on the German border where the brigade will be headquartered, adding "we hope you feel at home."

"The presence of American soldiers in Poland is another step in our strategy to ensure safety and security for Poland and the region," she added.

Hailing from Fort Carson, Colorado, the so-called "Iron Brigade" comprising some 3,500 soldiers and heavy equipment will also be deployed in NATO partners Estonia, Latvia, Lithuania, Romania, Bulgaria and Hungary on a rotational basis.

It is part of the Pentagon's "Atlantic Resolve" operation aimed at countering security concerns triggered on NATO's eastern flank by Russia's 2014 annexation of Crimea from Ukraine.

"This is America's most capable fighting force: a combat-ready, highly trained US armoured brigade, with our most advanced equipment and weaponry," US ambassador to Poland Paul Jones said at the ceremonies, also attended by hundreds of Zagan residents.

"This force embodies America's iron-clad committment to honour our NATO treaty obligation to defend our NATO allies."

The US troops and tanks began streaming into Poland Thursday as part of one of the largest deployments of US forces in Europe since the Cold War, an operation that Russia angrily branded a security "threat".

The brigade's deployment, ordered by the outgoing Obama administration, comes a week ahead of the inauguration of US President-elect Donald Trump, who has suggested his Republican administration will seek to ease tensions with the Kremlin.

Poland on Friday told Trump that any improvement in Washington's ties with Moscow cannot come at the cost of harming Warsaw.

- 'Safe Poland' -

According to Poland's Defence Minister Antoni Macierewicz, a total of 7,000 US and NATO troops will be stationed in his country in the coming years.

"We've waited decades for you, often feeling alone and that we'll never see you here," Macierewicz told US troops at the Zagan ceremonies.

The defence ministry held "Safe Poland" picnics Saturday in cities across the country, allowing average Poles to meet with Polish and newly deployed US troops, view military hardware and chow down typical Polish army grub including pea soup with ham.

Hundreds of residents attended the official welcome ceremonies in Zagan.

"The deployment is necessary and it's great that they're here. We can feel the support of our allies," a Zagan resident who identified himself only as Pawel told AFP.

Fellow Zagan resident Jan said he was not convinced the US deployment was absolutely necessary, but chuckled that "it would be good if they scare the Russians a little, because they're out of control".

Freshly-arrived US military policeman Peter Gomez told AFP he felt "very welcome" as he posed for selfies with Zagan residents.

"I'm surprised actually, people are very excited to see us."

Tensions between Russia and the West have escalated over the past two years, triggered by Russia's actions in Ukraine and its military campaign in Syria since late 2015.

Last summer, NATO leaders endorsed plans to rotate troops into Poland and the three Baltic states to reassure them they would not be left in the lurch if Russia was tempted to repeat its Ukraine intervention.