US President Joe Biden pledges unwavering support for Ukraine’s sovereignty and territorial integrity
Tensions have risen once again in the long-simmering conflict in eastern Ukraine, where government forces have battled Russian-backed separatists since 2014.
Reports this week swirled of Russian troop movements and an escalation of armed clashes, while Moscow and Kiev's Western allies exchanged warnings. Here's what we know:
What do we know about Russian troop movements?
Ukraine this week accused Russia of massing thousands of military personnel on its northern and eastern borders as well as on the Crimean Peninsula annexed by Moscow in 2014.
Kiev said that 28,000 separatist fighters and more than 2,000 Russian military instructors and advisers are currently stationed in eastern Ukraine, while nearly 33,000 soldiers are deployed in Crimea.
The Kremlin has repeatedly denied sending troops and arms to buttress pro-Russian separatists, but did not deny the recent troop movements, saying: "Russia is not threatening anyone."
What are Moscow and Kiev aiming for?
Observers say the reported Russian troop build-up is a test for US President Joe Biden, who caused an uproar in Moscow last month by agreeing with a description of his Russian counterpart Vladimir Putin as a "killer."
"The Russians are demonstrating that they are not afraid of anyone," Oleksandr Lytvynenko, head of the National Institute for Strategic Studies, told AFP, adding that Moscow wants to put "Ukraine in its place."
The move presents an opportunity for Ukrainian authorities to mobilize support from their Western allies and reaffirm Washington's support in particular after Donald Trump's presidency.
US President Joe Biden did just that on Friday, calling his Ukrainian counterpart Volodymyr Zelensky to pledge his "unwavering support for Ukraine's sovereignty and territorial integrity in the face of Russia's ongoing aggression."
What about the peace efforts?
A ceasefire brokered last July had brought relative calm to the conflict. But fighting escalated at the start of the year, with Moscow and Kiev blaming the other for the rise in violence between government forces and Kremlin-backed separatists in eastern Ukraine.
Kiev says 20 Ukrainian servicemen have been killed and 57 wounded since January.
The renewed conflict has brought into the spotlight the peace talks mediated by France and Germany in the Normandy format of countries that includes Ukraine and Russia.
Although in 2015 they agreed to the Minsk accords to reduce the fighting, little progress has been made in the years since. The last summit held in Paris in December 2019 did not produce concrete progress and no new meeting is planned.
What does the West say?
While the US is not a player in the peace process, Washington has warned Moscow against any attempt to "intimidate" Kiev.
Earlier this week the Pentagon said, US forces in Europe had raised their alert status following the "recent escalations of Russian aggression in eastern Ukraine."
Kremlin spokesman Dmitry Peskov on Friday said that Moscow would take necessary "measures" in the event of Western military interference in Ukraine.
For its part, Paris is taking a wait-and-see approach.
"There are obviously troop movements," said French European Affairs Minister Clement Beaune, but he added: "We do not know what that means."
What to expect?
Most observers dismiss the scenario of a Russian invasion of Ukraine.
The Russian troop movements "do not appear to be of the size indicative of an invasion, either from Crimea, or elsewhere," Michael Kofman, a senior fellow at the US-based CNA think-tank, wrote on Twitter.
Kiev-based analyst Lytvynenko shares that opinion but is worried about "a high risk of an uncontrolled development" of these "periodic escalations."
However, Timothy Ash, an analyst at the London-based BlueBay Asset Management group, raised the possibility of "Russian attacks around Crimea to secure fresh water supplies" for the peninsula that Kiev cut off.
But ultimately, said Russian military analyst Alexander Golts, Moscow uses tensions as "an instrument of diplomatic negotiation with the West."