With the West forced to contend with the looming threat of a Russian invasion of Ukraine, Moscow is asking that NATO rethink its deployment in the region.

As tensions rise, the countries concerned -- all of which were once under the Soviet yoke and border Russia -- are instead asking for a greater NATO presence.

Here are some facts and figures on the "enhanced forward presence" (EFP) deployment in Poland and the Baltic nations of Estonia, Latvia and Lithuania:

- Biggest reinforcement -

In 2017, NATO deployed four multinational battalions on a rotational basis to Poland and the Baltic states to guard against any possible Russian adventurism.

It was the biggest reinforcement of its collective defences since the Cold War.

Polish President Andrzej Duda hailed the launch of his country's battalion as an "historic moment" at the time.

Poland has been a NATO member since 1999 while the Baltic trio -- with a combined population of just six million people -- joined in 2004.

- Crimea -

NATO decided to send the military units to its eastern flank after Moscow annexed Crimea and helped separatists take over parts of eastern Ukraine in 2014.

The four countries, dominated by the Soviet Union for more than 40 years after World War II, had lobbied hard for the NATO deployments as an extra security buffer.

- Achilles' heel -

Poland has said the battle groups are notably necessary to help defend the "Suwalki Gap", a land corridor on the Polish-Lithuanian border that is sandwiched between Russia's heavily militarised Kaliningrad exclave and Belarus.

Military strategists warn it is the Achilles' heel of NATO's eastern flank: its capture would amputate the alliance's three Baltic members and so shatter its credibility.

- Troops -

The four NATO battalions based in Estonia, Lithuania, Latvia and Poland are led by Britain, Germany, Canada and the United States, respectively, with contributions from some 15 other member nations.

Each battlegroup comprises around 1,200 soldiers, though the numbers vary depending on the country and regularly change in accordance to deployment procedures.

The troops train constantly to improve coordination and conduct joint exercises.

Last year, Germany recalled an entire platoon of 30 soldiers stationed in Lithuania after its members were accused of racist and anti-Semitic behaviour.

- More please -

Faced with the latest threat from Moscow in the region, Poland and the Baltics have called for more support.

At a meeting with NATO Secretary General Jens Stoltenberg in November, Poland's Duda urged the alliance to send reinforcements to its eastern flank.

Estonian Prime Minister Kaja Kallas meanwhile called for a greater US presence in the Baltic states earlier this month.

There have even been calls for a permanent US presence. Polish officials have long raised the prospect, and previously pitched the idea of building a "Fort Trump" to house US soldiers.

NATO however promised Russia in 1997 not to set up permanent bases in the former eastern bloc.

- Russian demands -

Amid the current standoff over Ukraine, Moscow put forward demands last month for wide-ranging security guarantees from the West.

Those include the request that Ukraine never be allowed to join NATO, but also sticking points that directly affect countries like the Baltics and Poland.

In the draft document, Russia insisted that other alliance members "shall not deploy military forces and weaponry" in Poland and the Baltic states.

Russia said such deployments could be allowed "in exceptional cases to eliminate a threat to security" but only with Moscow's consent.