International politicians tried yesterday to get some kind of agreement on Ukraine but with little sign of success.

Russian Foreign Minister Sergei Lavrov began talks in Paris with his US and EU counterparts, with Russia maintaining that its main interest was in the security and safety of Russian-speaking residents.

The US and EU for their parts were claiming that diplomatic talks - plus a few sanctions directed at 18 prominent Russians - were the extent of their intentions.

But British Foreign Secretary William Hague spoke darkly of the "costs and consequences" if talks failed, while the US announced plans for more US and Nato military co-operation with Poland and the Baltic states adjacent to Russia.

The US assumed control over Nato air policing duties over Baltic countries Estonia, Latvia and Lithuania in January.

In Ukraine itself, the rump Kiev government denied the authority of exile President Viktor Yanukovych to authorise Russia to use its armed forces.

Ukraine's UN ambassador Yuriy Sergeyev said in a letter to the security council that under the constitution "the parliament of Ukraine has an exclusive power to approve a decision on the admission of foreign military forces."

Mr Sergeyev said he was responding to a statement "allegedly made by Mr Viktor Yanukovych."

But Russian troops seemed not to be of any real relevance in many other parts of Ukraine.

In Donetsk hundreds of demonstrators waving Russian flags stormed a government building for the second time. More than 2,000 people gathered outside the regional administrative building yesterday afternoon before groups of men broke through police ranks.

Several government buildings around Ukraine, particularly in the east, have been seized by pro-Russian demonstrators.

And in Crimea, pro-Russian demonstrators have been turning away families bringing supplies to Ukrainian troops refusing to surrender their bases.