Russia has deployed tens of thousands of troops near the Ukraine border, triggering the worst security crisis to emerge between Moscow and the West since the Cold War.

The West, led by the US, has thrown its weight behind Ukraine, which lost control of its Crimean Peninsula when Russia annexed it in 2014.

The Kremlin has justified its military muscle-flexing as an attempt to counter decades of NATO expansion in the region. Russia has demanded legally binding guarantees that the NATO alliance will not embrace Ukraine and other former Soviet nations, or place weapons there. It also wants NATO to pull back its forces from countries in Central and Eastern Europe that joined the alliance since the 1990s.

Russia has also been accused of backing armed separatists in eastern Ukraine. The conflict has left more than 13,000 people dead in nearly eight years of fighting. A 2015 peace deal brokered by France and Germany helped end large-scale battles, but a political settlement has stalled, and frequent skirmishes have continued along the tense line of contact.

In early 2021, a spike in ceasefire violations in the east and a Russian troop concentration near Ukraine ignited the invasion fears, but tensions abated when Moscow pulled back the bulk of its forces after manoeuvres in April.

The military buildup near Ukraine  resumed in late 2021, with Ukrainian and Western officials warning that the increased troop concentration could herald a multipronged Russian attack.

A convoy of Russian armoured vehicles moves along a highway in Crimea. [AP Photo]

Members of Ukraine's Territorial Defence Forces, volunteer military units of the Armed Forces, train in a city park in Kyiv. [Efrem Lukatsky/AP Photo]

A Russian soldier takes part in drills at the Kadamovskiy firing range in the Rostov region in southern Russia. [AP Photo]

Servicemen march leaving a memorial ceremony to honour the civilians who died during shelling at a crowded bus stop in 2015, in Donetsk, controlled by Russia-backed separatists in eastern Ukraine. [Alexei Alexandrov/AP Photo]

In 2014, Russia annexed the Crimean Peninsula after the overthrow of Ukraine’s Moscow-friendly leader. [Efrem Lukatsky/AP Photo]

Russia announced sweeping naval drills in several parts of the world this month and claimed the West is plotting "provocations" in neighbouring Ukraine where the Kremlin has been accused of planning aggressive military action. [Efrem Lukatsky/AP Photo]

Russian T-72B3 tanks take part in drills at the Kadamovskiy firing range in the Rostov region in southern Russia. [AP Photo]

Dozens of civilians have been joining Ukraine's army reserves in recent weeks amid fears of a Russian invasion. [Efrem Lukatsky/AP Photo]

A Ukrainian serviceman patrols a street near the front line with Russia-backed separatists in Verkhnotoretske village in Yasynuvata district, Donetsk region in eastern Ukraine. [Andriy Andriyenko/AP Photo]