No obligation to defend Ukraine from Russia, Nato chief says

"There's a difference between a partner Ukraine and an ally like, for instance, Latvia", he added.

"We need to understand the difference between a Nato ally, Latvia, other Baltic countries, Poland, Romania, and a close and highly-valued partner, Ukraine. We provide support for Ukraine ... for the Nato allies we have the security guarantees, Article 5", he reiterated.

Stoltenberg spoke at a meeting of Nato foreign ministers in Latvia amid a Russian military build-up on Ukraine's eastern border.

"We see [Russian] heavy armour, we see drones, and combat-ready troops [near Ukraine]", he said.

But his comments on Article 5 in the Nato treaty were a sign the Western alliance would not defend Ukraine in the event of an attack, just as it did not do so in Russia's first invasion of Ukraine in 2014, or Russia's invasion of Georgia, also a Nato "partner", in 2008.

Russia would still pay a "high price" for any fresh aggression, the Nato chief added.

But this would likely be limited to economic sanctions and additional defensive deployments on Nato's eastern flank, he indicated.

"There will be a high price to pay for Russia if they once again use force against the independent, sovereign nation Ukraine," he said on Tuesday.

"We have demonstrated our ability to impose costs, economic, political actions. And also, over the years, increased our military presence in this region," he added.

There would be "heavy economic and financial sanctions, political sanctions", he said.

Nato already had Russia-deterrent battalions in the Baltic Sea and Black Sea regions.

These are meant to act as 'tripwires' for up to 40,000 rapid-reaction forces in the event of war.

Latvia, Poland and Belarus

For its part, Latvia has called for US troops and Patriot missile batteries to be permanently stationed on its territory due to the increasingly tense climate.

And for his part, Russian president Vladimir Putin dialled up tension in remarks at an economic forum in Moscow also on Tuesday.

Nato military assistance to Ukraine was a "red-line" threat to Russia, he said.

"We can also do this [cause threats]. The flight time it takes to reach those who give orders [in Nato] is five minutes," he said, referring to the flight-time of a Russian hypersonic missile.

The Belarusian president, Alexander Lukashenko, said the same day that Crimea, which Russia annexed from Ukraine, was both "de facto" and "de jure" Russian territory.

His comments indicated he planned to recognise its annexation on an upcoming visit there, further jangling nerves in the region.

Lukashenko, last weekend, also said he would fight on Russia's side in any war with Ukraine and announced new military drills on Ukraine's border.

His Ukraine war-talk comes after recently pushing thousands of migrants to attack EU borders in Lithuania and Poland.

Poland also fears Russia will shortly build new military bases on the Belarus-EU border as part of the two countries' secret, joint "military doctrine".

"The Kremlin and its allies want to change the political system and destabilise the region," Polish prime minister Mateusz Morawiecki told the BBC on Tuesday.

"We have to wake up from our geopolitical nap," he added.