Ukrainian forces have fired mortar shells and grenades at multiple localities on the border with Russia, the Sputnick news agency claims.

“The Ukrainian military fired mortar shells and grenades at four localities in the self-proclaimed Lugansk People’s Republic at 2.30am GTM on Thursday, according to the Joint Centre for Control and Coordination,” the Russian news agency said on Thursday afternoon (Australian time).

Lugansk is in Ukraine’s east, in the country’s disputed Donbas region and the claims of attack came from Russian-backed rebels.

“Ukraine’s armed units grossly violated the ceasefire regime, using weapons that, in accordance with the Minsk agreements, should be withdrawn,” Sputnik quoted an LPR officer as saying.

Russia has massed more than 100,000 troops close to Ukraine’s borders while demanding that NATO pledge not to accept Kyiv as a member.

The West has threatened Moscow with new sanctions if it attacks Ukraine. Russia denies planning any attacks.

Sporadic shooting has been reported in the rebel-held regions from both sides in recent years. But an escalation in the years-long conflict with Donbas separatists could further fuel tension between Russia and the West.

The reports came as Western countries warned Russia’s military presence on Ukraine’s borders was continuing to grow. Estonia said battle groups were moving ahead of a likely attack to occupy “key terrain”, contradicting Moscow’s insistence of a pullback.

In rare public comments, Britains defence intelligence chief said more armoured vehicles, helicopters and a field hospital had been spotted.

A senior official in US President Joe Biden’s administration said up to 7000 more troops had moved to the border in recent days, including some arriving on Wednesday. However, he provided no evidence.

Western nations have suggested arms control and confidence-building steps to defuse the stand-off, which has prompted them to urge their citizens to leave Ukraine because an attack could come at any time. Russia has repeatedly denied any plans to invade.

Western nations have also said Russia might use false claims of an attack by Ukrainian forces to launch an invasion of its neighbour.

“There’s what Russia says. And then there’s what Russia does. And we haven’t seen any pullback of its forces,” US Secretary of State Antony Blinken told MSNBC on Wednesday.

“We continue to see critical units moving toward the border, not away from the border.”

Estonian intelligence was aware of about 10 battle groups of troops moving towards the Ukrainian border, where about 170,000 soldiers were already deployed, its intelligence chief Mikk Marran said.

The attack would include missile bombardment and the occupation of “key terrain”, he said.

“If Russia is successful in Ukraine, it would encourage it to increase pressure on the Baltics in the coming years,” he said.

“The threat of war has become the main policy tool for Putin.”

Russia’s defence ministry said its forces were pulling back after exercises in southern and western military districts near Ukraine, and Moscow’s ambassador to Ireland insisted forces in western Russia would be back to their normal positions within a month.

It published video that it said showed tanks, infantry fighting vehicles, and self-propelled artillery units leaving the Crimean peninsula, which Moscow seized from Ukraine in 2014.

But NATO military commanders are drawing up plans for new combat units that diplomats said could be deployed in Bulgaria, Romania, Hungary and Slovakia. Such units already exist in Poland and the Baltic states.

Ukraine also increased the number of border guards on its frontier with Belarus, Russia’s ally, where some 9000 Russian troops are estimated to be involved in military exercises.

President Volodymyr Zelenskiy, who is criss-crossing the country to help bolster Ukrainians’ morale, observed drills by his armed forces that included Javelin anti-tank missiles.

Wednesday was designated a patriotic holiday in response to reports Russia could invade on that day.

“No one can love our home as we can. And only we, together, can protect our home,” Mr Zelenskiy said.

People raised flags and played the national anthem to show unity against fears of an invasion.

The government said a cyberattack that hit the defence ministry was the worst Ukraine had seen, pointing the finger at Russia, which denied involvement.

US officials were as yet unable to say who was responsible, White House spokesperson Jen Psaki said.

NATO said it could prove Russia’s failure to pull back its soldiers with satellite imagery.

“More troops are on their way,” Secretary-General Jens Stoltenberg said.

Moscow has accused the West of hysterical war propaganda after repeated warnings of a possible attack.

Russia sees Ukraine joining NATO as a threat to its security and has said it is ready to reroute energy exports to other markets if it is hit by sanctions, which Washington and its allies have threatened if it invades.

Despite the war of words, diplomatic efforts continue.

Mr Biden and German Chancellor Olaf Scholz underscored the “importance of continued transatlantic coordination” on a call on Wednesday, the White House said.

Ukraine has asked the UN Security Council to discuss on Thursday a bid by Russia’s parliament to recognise self-proclaimed separatists.

British Foreign Secretary Liz Truss is due to visit Kyiv this week and Mr Blinken will travel to Germany for the Munich Security Conference, which starts on Friday, to co-ordinate with allies.

-with AAP