The world's top diplomats have converged in the French capital Paris in an effort to cool the crisis in Ukraine, as Russia continues to deny deploying troops in Crimea.

The US secretary of state, John Kerry, and his Russian counterpart, Sergey Lavrov, will on Wednesday meet face-to-face for the first time since the crisis escalated, after a conference attended by the five permanent members of the UN Security Council.

Lavrov is also expected to meet his Ukraine counterpart, Andrey Deshchitsia, later in the day at separate talks, which the US and Britain hailed as an opportunity for "direct communication".

Following his meeting with Kerry and Britain's Foreign Secretary William Hague, Deshchitsa said: "Today the Ukrainian future will be decided ... We want to keep neighbourly relations with the Russian people. We want to settle this peacefully."

During the meeting they also agreed that direct talks between Kiev and Moscow were crucial to resolving tensions, and called for the immediate deployment of international monitors in the Crimean region.

Earlier on Tuesday in Madrid, Lavrov has said his country could not order the "self defence" forces in Ukraine's Crimea back to their bases because the troops do not answer to Moscow.

Lavrov repeated Russia's assertion that armed men deployed there are not Russian forces and said that Russia's Black Sea naval personnel were in normal positions.

Lavrov vowed to prevent bloodshed in Ukraine, including attacks against its own citizens.

"We will not allow bloodshed. We will not allow attempts against the lives and well-being of those who live in Ukraine and Russian citizens who live in Ukraine," Lavrov told the news conference.

He also said it was up to the Crimean and Ukrainian authorities to grant international observers access.

Back in Paris, French Foreign Minister Laurent Fabius said everyone had been working non-stop for a diplomatic solution.

"We have a principle of firmness but at the same time of searching for dialogue," Fabius said, as he stood alongside his Ukrainian counterpart, who was making his first trip abroad in the new post.

While diplomats seek a political solution to the deadlock, Ukraine's economy has been given a much needed boost, as the European Commission announced an aid package worth at least $15bn.

Nearing bankruptcy

Wednesday's gathering, originally scheduled to deal with the Syrian refugee crisis, came a day after the Russian president, Vladimir Putin, appeared to step back from the brink of war. But the crisis is far from over.

Ukraine is near bankruptcy and the European Union's executive arm was supposed to decide on Wednesday on a package of support measures to add to the $1bn aid package promised by the US.

Putin does not recognise the new Ukrainian leadership in Kiev, which in turn accuses Russia of a military invasion in Crimea.

Troops believed to be Russian took over Crimea on Saturday, placing forces around its ferry, military bases and border posts.

A spokesman for Ukraine's defence ministry told the AFP news agency on Wednesday that Russian forces seized part of a Ukrainian missile defence unit.

The command post and control centre of the base in Evpatoria, on the western coast of Crimea, however remained under Ukrainian control, the source said.