Russia may deny any plans for invasion but it has carved out a series of demands from the West that cannot be met. What happens next could jeopardise Europe's entire security structure.

Why is Russia threatening Ukraine?

Russia has long resisted Ukraine's move towards European institutions, and Nato in particular. Its core demand is for the West to guarantee Ukraine will not join Nato, a defensive alliance of 30 countries.

Ukraine shares borders with both the EU and Russia, but as a former Soviet republic it has deep social and cultural ties with Russia, and Russian is widely spoken there.

The threat is being taken seriously because Russia has invaded Ukraine before.

When Ukrainians deposed their pro-Russian president in early 2014, Russia annexed Ukraine's southern Crimean peninsula and backed separatists who captured large swathes of eastern Ukraine. The rebels have fought the Ukrainian military ever since in a conflict that has claimed more than 14,000.

How big is the risk of invasion?

Russia says it has no plans to attack Ukraine: and armed forces chief Valery Gerasimov even denounced reports of an impending invasion as a lie.

Nato's secretary general warns the risk of conflict is real, but US officials have stressed they do not believe Russia has decided on an invasion, and it is not imminent. Ukraine's president has appealed to the West not to spread "panic".

However, President Vladimir Putin has threatened "appropriate retaliatory military-technical measures" if what he calls the West's aggressive approach continues.

The US says Russia has offered no explanation for the troops posted close to Ukraine - and thousands of Russian troops have headed to Belarus, close to Ukraine's northern border, for exercises.

Russia's deputy foreign minister compared the current situation to the 1962 Cuban missile crisis, when the US and Soviet Union came close to nuclear conflict.

Western intelligence suggests a Russian incursion or invasion could happen some time in early 2022. President Biden's top military officer, Gen Mark Milley, said that the scale of the Russian forces would cause a significant amount of casualties and fighting in urban areas would be horrific.

Can Russian action be stopped?

President Putin has spoken several times to Mr Biden and high-level talks continue. He has expressed hope that a solution can be found, but Russian officials have warned that Western rejection of their key demands is leading to a "dead end".

The question is how far Russia will go. President Biden has warned that a full-scale invasion would be a disaster for Russia. But if it was a minor incursion, he said controversially that the West would "end up having to fight about what to do".

The White House has stressed any move across the border constitutes a renewed invasion - but points out Russia has other weapons, including cyber-attacks and paramilitary tactics. When 70 Ukrainian government websites went down in January, Russia denied Ukrainian accusations that it was behind the attack.

Russia has more weapons than Ukraine, But that does not guarantee they'd win.

Abeg, where's Nigeria's own, who got their Data ? I want to check how many troops, war tanks & ballistic missile we have