A group of 300 US paratroopers arrived in Ukraine to train with Ukrainian national guard units, in a move the Kremlin warned could "seriously destabilise" the country, where pro-Moscow rebels are battling Kievan forces in the east.

The paratroopers from the 173rd Airborne Brigade arrived in Lviv today (April 17), where they will train three battalions of Ukrainian troops over the next six months in nearby Yavoriv, said a US Army statement.

In Moscow, Russian president Vladimir Putin's spokesman Dmitri Peskov warned that the move "is a long way from helping towards a settlement of the conflict", according to a report by Russia's RIA Novosti news agency.

"On the contrary, it can seriously destabilise the situation," he said.

Earlier this week, fighting between rebels and Ukrainian forces resumed near Donetsk, breaking a day long ceasefire agreement.

A Ukrainian military spokesman said six troops had been killed and 12 wounded in 24 hours.

A formal ceasefire agreement agreed in February has been broken several times.

In recent months, Ukrainian forces have suffered a series of setbacks at the hands of pro-Moscow fighters, and are reportedly demoralised as well as ill-equipped.

On Thursday, April 16, in a live call in with the Russian public, Putin denied that he was arming the rebel groups in east Ukraine, and accused Kiev of forming an economic blockade around rebel-held areas.

Russia has accused the West of instigating the protests which saw pro-Moscow Ukrainian President Viktor Yanukovich ousted from power last year.

Ukraine's national guard consists of volunteer units, which are now integrated with the Ukrainian national army.

The year-long conflict between the Ukrainian government and rebel groups has so far claimed 6,000 lives and devastated the eastern industrial heartland of Ukraine.