Speaking at an event in Brussels, NATO Secretary General Jens Stoltenberg said on Friday that the build-up of Russian troops at the borders with Ukraine and Belarus is not necessarily the only way Moscow plans to put pressure on Western allies.

"We need to be prepared for a wide range of different forms of aggression," he said, listing several examples.

It comes as Sky News' international editor Dominic Waghorn asked Ukraine's President Volodymyr Zelenskyy whether he was playing down the threat of an imminent invasion to protect his country's economy and that the US was right to claim that a major border offensive was a "real possibility".

The leader replied: "The question of the possible escalation is not less acute as (it is) for the US and other partners."

But he added the conflict with Russia has been going on since 2014, saying Ukraine "has been in this situation for eight years so we should be looking up but also looking on the ground".

"We may lose the economy of our country, people come first. The probability of the threat is there. In 2021 it was the same, in 2020 it was less," he said.

He continued: "Yes, it (an invasion) may happen unfortunately, but let's put three dots here, not just one full stop and say 'yes for sure it will happen'."

'No tanks in the streets'

Speaking to reporters in Kyiv, he also said Ukraine was not a sinking Titanic and accused Washington and the media of fuelling panic that weighed on the economy while there were "no tanks in the streets".

Mr Zelenskyy said the White House was making a "mistake" by highlighting excessively the risk of a large-scale war, and this was the message he gave President Joe Biden in their phone call on Thursday.

During the news conference, he said his country needed $4bn-5bn (£3bn-£3.7bn) to stabilise the economy, including through foreign investments, as he welcomed a €1.2bn (£1bn) EU aid package.

Meanwhile, Russia has launched a series of military drills near its border with Ukraine and also plans similar exercises in neighbouring Belarus.

The Kremlin is thought to be mobilising infantry and artillery units in southwestern Russia, alongside war planes in Kaliningrad on the Baltic Sea and warships in the Black Sea and Arctic.

NATO has bolstered its presence in the Baltic Sea region in response, while the US has ordered a further 8,500 troops to be on high alert for deployment to eastern Europe.

A Russian troop build-up along its Ukraine border includes supplies of blood for the wounded, three US officials told the Reuters news agency.

Russia has repeatedly insisted it will not invade Ukraine, but foreign minister Sergei Lavrov warned on Friday: "There won't be a war as far as it depends on the Russian Federation, we don't want a war.

"But we won't let our interests be rudely trampled on and ignored."

Putin tells Macron Moscow's principal concerns not met

In a phone call with French President Emmanuel Macron on Friday, Vladimir Putin said that the US and NATO's proposals on security do not meet Moscow's main concerns.

But the Kremlin said Mr Putin would closely study the proposals before deciding on further action.

A build-up of as many as 150,000 Russian troops on the Ukrainian border began late last year as Russia demanded that Ukraine be banned from joining NATO and the alliance scales back its military operations in eastern Europe.

Moscow wants to keep its former Soviet neighbour in its 'sphere of influence' following its illegal annexation of Crimea in 2014.

Negotiations between Russia and the West last week proved largely unsuccessful, with US President Joe Biden telling Ukraine's President Zelenskyy in a phone call on Thursday that Russia could invade as soon as next month.

The US and NATO formally rejected Russia's demands this week but outlined a number of secondary areas where there could be room for negotiation and an opportunity to avoid full-scale war.

Russia faces devastating sanctions - including halt to gas pipeline

Meanwhile Washington and other Western allies warned the Kremlin it faces devastating economic sanctions if it decides to pursue military intervention.

US officials said Germany would not allow the newly-constructed Nord Stream 2 pipeline to bring gas from Russia if it goes to war.

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And Whitehall sources have told Sky News that Britain is considering sending "hundreds more" troops to the Ukrainian border to bolster NATO's presence.

But despite the possibility of an imminent invasion, Ukrainian officials have tried to convey a sense of calm.

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Its defence minister Oleksii Reznikov told parliament on Friday that the total number of Russian troops near Ukraine is comparable to Moscow's military build-up in the spring of 2021, when it eventually decided to pull its forces back.

"We haven't observed any events or actions of military character that significantly differ from what was going on last spring," with the exception of the deployment to Belarus, Reznikov said.