U.S. troops will remain in Poland and the Baltic states through 2015 "to deter Russian aggression," the top U.S. commander for Europe said on Sunday.

"There are going to be U.S. army forces here in Lithuania as well as Estonia and Latvia and Poland for as long as it's required to deter Russian aggression," said Lt. General Ben Hodges, commander of U.S. Army Europe.

Not long ago, the cadets at the military academy in east Ukraine's industrial hub of Donetsk swore allegiance to the Ukrainian flag.

Now, as fighting rumbles on between between pro-Russian insurgents and government forces, they are pledging an oath of loyalty to the rebels' self-proclaimed Donetsk People's Republic (DNR).

Dutch experts on Sunday completed the recovery of wreckage from the crash site of downed Malaysia Airlines flight MH17 in eastern Ukraine and have sent it to a government-controlled city en route for the Netherlands

"(Transport of) the recovered wreckage from flight MH17 is under way towards Kharkiv," by train, the Dutch Safety Board (OVV) said in a statement.

When Ukraine pulled out of its association agreement with the European Union a year ago, kicking off its revolution, it took Brussels by surprise.

Twelve months later the EU is still learning bitter lessons about geopolitics and Russian aggression, experts say.

Russia on Saturday accused the West of seeking regime change in Moscow, raising tensions over the conflict in Ukraine in the worst crisis in relations since the end of the Cold War.

Foreign Minister Sergei Lavrov spoke out against Western sanctions on Russia after U.S. Vice President Joe Biden hinted Friday at possible further measures over its "unacceptable" role in the former Soviet state.

Russia has 7,500 troops in the east of the country, where pro-Moscow separatists have been fighting government troops for months, Ukraine's defense minister said.

"Unfortunately, the stabilization of the situation in the east of Ukraine does not depend only on us," Stepan Poltorak said in a statement posted on the ministry's website on Saturday.

Ukraine's new coalition government declared joining NATO a priority Friday in a move likely to provoke fresh Russian anger as thousands gathered in Kiev to mark the first anniversary of protests which unleashed a year of turmoil.

A crowd of several thousand gathered in Kiev's Independence Square, known as Maidan, late Friday to remember the more than 100 protestors who died in demonstrations that started on November 21 last year. 

U.S. Vice-President Joe Biden warned on a visit to Kiev Friday that Russia risked further isolation over its "unacceptable" aggression in Ukraine.

"It's simply unacceptable in the 21st century for countries to attempt to redraw borders by force... because they don't like a decision their neighbor has made," he said after meeting Ukrainian President Petro Poroshenko.

The symbols of Ukraine have been hidden somewhere in the school in the country's war-torn east -- but the headmistress will not say exactly where.

One year after the start of protests in Kiev that toppled a pro-Russian government and set in motion a chain of events that set off a bloody pro-Russian rebellion, at school Number 33 in insurgent-held Donetsk, all signs of Ukraine have been assiduously removed.

Ukraine's military on Friday accused Russia of shelling its territory for the first time since the signing of a nominal ceasefire in early September.

"Over the past day, for the first time since the signing of the Minsk agreement, the shooting of Ukrainian territory restarted from the side of the Russian Federation," said Ukrainian military spokesman Andriy Lysenko.