German Chancellor Angela Merkel warned Wednesday against severing ties with Russian President Vladimir Putin over the Ukraine crisis but said he must also do his part.

Merkel told the Saechsische Zeitung newspaper she was "working very hard to keep the lines of communication open" with Putin despite the EU's decision last month to level sanctions against Russia over its actions in the ex-Soviet state.

Moscow police on Tuesday detained dozens of protesters who had gathered outside the Ukrainian embassy to show their support for Kiev in its campaign against pro-Russian insurgents in the separatist east.

The private Moscow Echo radio station said about 200 people gathered for the demonstration before being dispersed by the police.

Russia will not pay for the Mistral warships being built by France until both ships have been delivered, an official said on Tuesday.

A convoy of 262 Russian trucks rolled toward the Ukrainian border on Tuesday as Kiev vowed to block the aid mission from its territory over fears it was a ploy to bolster pro-Kremlin rebels.

The convoy of what Russia says is humanitarian aid has sparked fears of an escalation in a conflict that has left hundreds dead in eastern Ukraine in recent months and plunged Moscow's ties with the West to their lowest point in decades.

European Commission head Jose Manuel Barroso warned Russian President Vladimir Putin in a phone call Monday against any unilateral intervention in Ukraine, including for humanitarian reasons.

"Speaking with President Putin, President Barroso said that the EU would join in international efforts to assist people in need as a result of the conflict," a commission statement said.

The Kremlin said Monday that Russia was sending a "humanitarian convoy" to eastern Ukraine despite Western fears that the mission might be used as a cover for intervention.

"The Russian side is sending a humanitarian convoy to Ukraine in cooperation with representatives of the International Committee of the Red Cross," President Vladimir Putin told European Commission head Jose Manuel Barroso on the phone, according to a Kremlin statement.

Scores of panicked inmates escaped when shells rained down on a high-security prison in eastern Ukraine during heavy fighting between government forces and pro-Moscow rebels, authorities said Monday.

Ukraine's military meanwhile reported six soldiers killed in the last 24 hours as its forces try to retake the main separatist bastions of Donetsk and Lugansk, bringing Kiev's death toll to 568 troops in four months of fighting.

Dutch air crash investigators said Monday they expect to release an initial report into what brought down flight MH17 over Ukraine with the loss of 298 lives "in a few weeks".

There were 193 Dutch citizens aboard the Malaysia Airlines 777 when it exploded over strife-torn eastern Ukraine on July 17 and the Dutch are in charge of victim identification and probing the cause of the disaster.

Over 100 inmates broke out of jail when shells rained down on a high-security prison in the besieged rebel stronghold of Donetsk in east Ukraine, killing one, local authorities said Monday.

Mortar blasts rocked the correctional facility in a western district of the city Sunday evening, hitting the living areas, administrative headquarters and an electrical substation, the city council said in a statement.

Hollywood tough guy and musician Steven Seagal played a weekend concert in the Black Sea peninsula of Crimea, appearing on a stage adorned with the flag of pro-Russian separatists in Ukraine.