Nearly 300 U.S. paratroopers will begin training Ukrainian national guard soldiers next month, the Pentagon said Thursday.

The 290 paratroopers from the 173rd Airborne Brigade Combat Team, dubbed Sky Soldiers, will train the Ukrainian troops in the western town of Yavoriv.

Seventy years ago they crushed Nazi Germany together but raging tensions over Ukraine mean Russia's former World War II allies in the West will snub the Kremlin's showcase victory anniversary celebrations.

As top Western leaders give President Vladimir Putin's Red Square parade on May 9 the cold shoulder, the guest list of those likely to be coming -- including China's president and North Korea's reclusive leader -- shows how Moscow's international standing has shifted.

Human Rights Watch on Thursday accused both government and rebels forces of using cluster bombs in eastern Ukraine, with at least 13 civilians killed by the weapons since the start of the year.

"Using cluster munitions shows utter disregard for civilians," said Ole Solvang, senior emergencies researcher at Human Rights Watch (HRW).

British troops have begun a training mission in Ukraine, helping government forces fighting pro-Russian separatists, the Ministry of Defense in London said Thursday.

The BBC reported that 35 personnel are in the southern city of Mykolaiv as part of a two-month mission, although the ministry spokeswoman declined to confirm the details.

U.S. President Barack Obama and German Chancellor Angela Merkel spoke by telephone Wednesday on Ukraine, stressing they would keep up sanctions on Russia over its role in the crisis.

"There will be no easing of sanctions imposed on Russia until it has fulfilled all of its Minsk commitments," the White House said, referring to a recent deal to defuse tensions in eastern Ukraine.

Russian President Vladimir Putin on Wednesday triumphantly joined tens of thousands of supporters to mark one year since his takeover of Crimea, a seismic shift that shattered ties with Ukraine and the West.

Putin appeared on stage in front of a flag-waving crowd at a celebratory concert by the walls of the Kremlin to make an impassioned justification for seizing the Black Sea peninsula in a move that sent his poll ratings soaring.

Crises have a way of focusing minds. So it was with Eskander Budzhurov's 80-year-old mother when her son left the Crimean peninsula in a rush after it was annexed by Russia from Ukraine a year ago.

Budzhurov, a spry owner of a booth selling traditional Crimean Tatar snacks in Kiev, laughs as he recalls the mad dash to make his mother Skype-savvy before setting off with two sons for a new life, 800 kilometers (500 miles) away in the Ukrainian capital.

Russia on Wednesday signed a wide-ranging alliance with Georgia's breakaway region of South Ossetia that will further cement its control over the territory despite fierce condemnation from the West.

President Vladimir Putin inked a deal in Moscow with South Ossetian leader Leonid Tibilov that officially makes Russia responsible for defending the self-declared republic, where the Kremlin has stationed thousands of troops since a war with Georgia there in 2008.

Russia and pro-Moscow rebels on Wednesday condemned Ukraine for ratifying two bills on greater autonomy for the separatist east, saying they violated a peace deal and threatened a shaky month-long truce.

The latest wrangling over the east Ukraine peace plan came as Moscow celebrated one year since the annexation of Ukraine's Crimea peninsula, a key moment in the crisis that shattered ties with Kiev and the West.

Russia has stepped up military activity to pressure EU leaders who are set to consider fresh sanctions against Moscow, Polish Prime Minister Ewa Kopacz said Tuesday.

Russian President Vladimir Putin ordered massive military maneuvers on Monday, including the deployment of nearly 40,000 troops in the Arctic.