On the frontline in Ukraine's east, battle-weary soldiers are sceptical that US sanctions against Moscow and Kiev's appeal for NATO help will deter Russian President Vladimir Putin.

Faced with the largest deployment of Russian troops on Ukraine's borders since 2014, President Volodymyr Zelensky has requested more tangible help from the West, but many Ukrainian troops say they know they are on their own.

"We should only count on ourselves," Taras Mykytsey, a 52-year-old soldier, told AFP in the frontline village of Zaytseve north of the separatist stronghold Donetsk.

The separatists, who have carved out two "People's Republics" in eastern Ukraine, are backed by Russia.

"While we are waiting for something to be sent to us, Putin will not wait," added Mykytsey, sporting a helmet and a bulletproof vest.

Yuriy, a 29-year-old senior sergeant based near the town of Shchastya in the neighbouring Lugansk region, struck a similar note, saying he did not expect Western boots on the ground any time soon.

"What foreign country would want to send its people to their death?" he said.

Yuriy, who declined to give his last name, added that the Russian president would not buckle.

"Sanctions and negotiations, can, of course, restrain Russia a little, but in general, these negotiations for Putin, it's like throwing sand against the wind," he said.

US President Joe Biden has pledged his "unwavering support" to Zelensky, and Washington this week hit Moscow with new sanctions over US election interference and other hostile activity.

After talks in Paris on Friday with French President Emmanuel Macron and German Chancellor Angela Merkel, the Ukranian leader called for a four-way summit with Putin and the resumption of a ceasefire upended by a recent spate of clashes between Kiev troops and the separatists.

Under a grey spring sky, birdsong can be heard on the frontline but the tranquil spell cannot mask a spike in tensions and near daily clashes.

Around 30 Ukrainian troops have been killed since the start of the year, compared to 50 last year. Most of them were victims of sniper fire.

This week, "a soldier was killed and two others from our battalion were wounded” in an explosion, said 43-year-old Yuriy, speaking to AFP in the trenches near Zaytseve.

Yuriy, who also declined to give his last name, said the explosion was caused by a Russian-made landmine.

The Ukrainian military accuses Moscow of seeking to provoke a situation that would justify an armed operation.

"The enemy’s task is to cause as many losses as possible and provoke return fire,” Viktor Ganushchak, the deputy commander of Ukraine’s military operation in the east, told AFP in the town of Avdiivka, some 6 kilometres north of Donetsk.

Russia has denied sending weapons and soldiers across the border and says its troop movements do not pose a threat to anyone.

More than 13,000 people have been killed in a conflict which broke out after a popular uprising in Kiev ousted a Kremlin-backed president and Moscow moved to annex Crimea in 2014.

Some Ukrainian soldiers were hard-pressed to explain the Russian show of muscle, with others dismissing it as mere sabre-rattling.

"If it were an assault, it would be done more quietly without so much fuss,” said Yuriy, the senior sergeant.

Mykytsey said Russia’s plans were anyone’s guess.

"Are they preparing for an assault or are these military exercises?” he said.

"Our task is to prevent them from going any further. We have people and there are enough weapons.”

Over the past seven years, Ukraine has overhauled its army thanks to Western help, and Kiev’s battle-hardened soldiers say they are ready for a repeat of Moscow’s 2014 aggression.

"We are ready for any scenario,” said Ganushchak. "This is our land, we will defend it.”