Troops from the United States 82nd Airborne Division have landed at Rzeszow-Jasionka airport in southeastern Poland, with approximately 1,700 more set to join them shortly.
The first US troops reinforcing NATO allies in Eastern Europe amid a Russian military build-up on Ukraine's border have arrived in Poland.
A small plane carrying what a Polish military source said were US chain of command personnel landed on Saturday at Rzeszow-Jasionka airport in southeastern Poland, near the border with Ukraine.
"As announced, the first elements of the brigade battle group from the 82nd Airborne Division of the United States Army have arrived in Poland," a Polish military spokesperson said.
TV footage showed temporary accommodation being prepared at the G2A Arena in the nearby town of Jasionka, while workers could be seen building a fence around the venue.
About 1,700 service members, mainly paratroopers from the 82nd Airborne Division, will deploy from Fort Bragg, North Carolina, to Poland "over the next days", US Army sources have said.
On Wednesday, US President Joe Biden ordered nearly 3,000 extra troops to Poland and Romania to shield Eastern Europe from a potential spillover from the Ukraine crisis.
According to the Pentagon, a Stryker squadron of around 1,000 US service members based in the German town of Vilseck will be sent to Romania.
The first additional US troops arrived in Germany on Friday.
Russia has denied plans to invade Ukraine but Western capitals have accused Russia of amassing some 100,000 troops near Ukraine's borders.
Russia has also threatened to take unspecified military measures if its demands, including a permanent ban on Ukraine joining NATO, are not met.
The new plan goes above and beyond the 8,500 troops the Pentagon put on alert last month to deploy to Europe if needed.
NATO defence ministers are expected to discuss further reinforcements at their next meeting on February 16-17.