Tensions in Eastern Europe between Russia and NATO continue to escalate as both sides boost their military presence in the region.
Russia has said that a NATO deployment that has brought US troops into Poland is a threat to its national security.
Nearly four thousand troops will be positioned across Poland and the Baltic states. The deployment includes 87 tanks and 144 armoured vehicles. It's designed to reassure the US's European allies after Russia's annexation of Crimea in 2014.
Around 2,700 troops arrived in Poland on Thursday as part of operation Atlantic Resolve, with the rest expected to arrive at a later date.
"The main goal of our mission is deterrence and prevention of threats," US Army Colonel Christopher R. Norrie, commander of the 3rd Armoured Brigade Combat Team, said at a welcome ceremony in Poland's western city of Zagan.
In addition to Poland, former Soviet republics in the Baltic region have also requested US and NATO troops following the annexation of Crimea.
‘Threat' to Russia
The Kremlin, which has previously criticised NATO for its reinforcement in Eastern Europe, said on Thursday the deployment was an aggressive step along its borders.
"We consider this a threat to us," Dmitry Peskov, Kremlin's spokesman, told journalists on a conference call. "We are talking here about a third country stepping up its military presence in Europe near our borders."
Moscow has already deployed in retaliation nuclear-capable Iskander missiles in its European exclave of Kaliningrad, in a move the US State Department said was "destabilising to European security."