A tiny Russian "exclave" bordered by Poland and Lithuania could become the latest flashpoint amid rising tensions with Europe and the US, as a military build-up in the region intensifies.

Kaliningrad Oblast is a 15,000 square kilometre area of Russia home to its Baltic naval fleet and only year-round ice free port.

It's one of three main naval bases for the country along with others in Crimea and Syria, sparking fears it could be next in line for a proxy conflict as tensions between Russia and the West reach their highest point since the Cold War.

Russia has recently moved two battleships and parked nuclear-capable Iskander missiles in Kaliningrad for the first time since 2014, rattling the nerves of neighbours.

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This week the NATO and the UK hit back with a huge escalation of their own forces including tanks, troops and fighter planes.

On Wednesday, the UK announced it would send tanks, planes and troops to Estonia and Romania as part of a huge boost in defence spending and military build-up along Russian borders.

Defence Secretary Michael Fallon said fighter planes would be sent to a Romanian base in the Black Sea for four months from next May. Tanks, drones and 800 troops will also go to Estonia as part of an 8000 strong build-up of NATO allies that "battle ready" US troops.

"Backed by a rising defence budget this deployment of air, land and sea forces shows that we will continue to play a leading role in NATO, supporting the defence and security of our allies from the north to the south of the alliance," Mr Fallon said.

NATO Secretary-general Jens Stoltenberg confirmed NATO is watching two Russian warships that have recently moved to the Baltic Sea.

After a conference with members of the alliance responsible for protecting nearly one billion people he said European countries from Albania to Slovenia, France, the Netherlands, Germany and Norway will contribute to troop build ups in Lithuania and Poland.

"Our forces will be truly multinational. Sending an unmistakeable message: NATO stands as one. An attack on any ally will be considered an attack on us all."

He said NATO is not looking for trouble but must respond to Russian actions.

"We don't want a new cold war and we don't want a new arms race and therefore, what NATO does is defensive and it is proportionate," he said.

"At the same time, NATO has to react when we, over a long period of time, have seen a substantial military build-up by Russia and we have seen them modernise their military capabilities and most importantly, we have seen them willing to use military force against neighbours: Crimea, Ukraine - but also Georgia has also seen a threatening rhetoric from Russia.

"We are concerned about Russia's behaviour. But dialogue is even more important when tensions run high."

THE WAR GAMES

Kaliningrad's neighbour Poland has also reported a rise in citizen militias as people become concerned about rising tensions. Germany and Russia have also held individual "war games" to prepare for the event of an attack with the Russian version involving millions of citizens conducting first aid and military exercises.

News of the build-up comes after hacked emails were released that were purportedly from Russian President Vladimir Putin's adviser in Ukraine, Vladislav Surkov, and pro-Russian rebels in the region.

The files - released by Ukrainian group CyberJunta, which is affiliated with security services in the country - appear to show the close relationship between Surkov and rebels.

Russia has moved nuclear-capable Iskander ballistic missiles into Kaliningrad with one official saying Russia appears eager to dominate that body of water. Photo / AP
Russia has moved nuclear-capable Iskander ballistic missiles into Kaliningrad with one official saying Russia appears eager to dominate that body of water. Photo / AP

They reportedly detail communication around the annexation of Crimea and ask for the approval of rebel leaders and spending for press communications and a media centre from the Kremlin.

Kremlin Spokesman Dmirty Peskov denied they are genuine and said Surkov does not use emails. However at least two people who have had files included in the cache have confirmed they match the originals.

Former NATO Secretary General Anders Fogh Rasmussen told The Times it is the "clearest indication yet of high level Russian involvement in the organisation of the separatist Republics".

Last month a damning report into the downed airline MH17 showed that the Buk missile used to shoot down the plane arrived in Ukraine from Russian territory and was returned to it afterwards.