Ukraine urges swift action to 'deter' Russian invasion

Western countries have raised the alarm this month over reported Russian military activity near Ukraine, with the United States saying it has "real concerns" over a new troop build-up on the border.

"It's better to act now, not later" to "deter Russia", Ukrainian Foreign Minister Dmytro Kuleba said at a briefing for foreign media.

"What we are seeing is very serious. Russia has deployed a large military force in regions close to Ukraine's state border."

He said that Moscow has massed 115,000 troops around Ukraine, on the Crimean peninsula -- which Russia annexed in 2014 -- and in two eastern regions occupied by pro-Russian separatists.

Tanks, artillery, electronic warfare systems and air and naval forces had also been deployed, he added.

"If Russia decides to undertake a military operation, things will happen in literally the blink of an eye," the foreign minister told reporters.

But he added that Ukraine, whose army has become "incomparably stronger" than when breakaway fighters in 2014 seized the Donetsk and Lugansk regions in a simmering conflict that has claimed more than 13,000 lives, would "fight back".

Kiev and its Western allies accuse Russia of sending troops and arms to support the separatists, claims Moscow denies.

After an uptick in violence at the beginning of the year, Russia massed around 100,000 troops on Ukraine's borders in the spring, raising fears of a major escalation.

Russia later announced a pullback but both Ukraine and its ally the United States said at the time the withdrawal was limited.

Ukraine, the United States, NATO and the European Union have raised the alarm about new Russian troop movements in recent weeks and warned about a possible invasion.

Moscow has dismissed the claims, accused Kiev of "provocations" and blamed Washington for escalating tensions in the region.