BERLIN (REUTERS, AFP) - Germany, France and Britain expressed alarm over mounting tensions in Ukraine's Crimea and called on Russia to de-escalate the situation, following reports that Moscow could have sent 6,000 troops to the region.

German Foreign Minister Frank-Walter Steinmeier warned on Saturday that developments in Ukraine over the past few hours were dangerous and urged Russia to explain its intentions regarding its troops in the Crimea region.

"The situation in Crimea in particular has become considerably more acute. Whoever pours more oil onto the flames now, with words or actions, is consciously aiming for further escalation of the situation," he said.

"Everything Russia does in Crimea must be in keeping with the sovereignty and territorial integrity of Ukraine, and treaties on Russia's Black Sea fleet," he said.

"We are holding the Russian government to its public statements on this. And this entails also that Russia provides without delay complete transparency over the movements of its troops in Crimea, as well as its goals and intentions behind these."

Meanwhile, French Prime Minister Jean-Marc Ayrault said the territorial integrity of Ukraine "must absolutely be respected".

"There is a requirement that must absolutely be respected - the territorial integrity of the country," Ayrault told reporters, speaking during a congress of European social-democrats in Rome.

"Everything must be done for this integrity to be totally respected.

"This requires a great sense of responsibility from all the players, above all from the political forces in Ukraine themselves but also from all of Ukraine's partners," Ayrault said.

"Ukrainians want democracy and we can understand that. They are turning to Europe, to European democracies. It is Ukrainians who must build their future," he said.

French Foreign Minister Laurent Fabius also said that France was "deeply concerned" over reports of significant troop movements in the flashpoint Black Sea peninsula.

"We call on the parties to abstain from actions that could raise tensions and harm Ukraine's territorial integrity," Fabius said in a statement.

British Foreign Secretary William Hague took to the social media on Saturday and said he had spoken to Russian Foreign Minister Sergei Lavrov to call for a de-escalation of the situation in Ukraine's Crimea.

"Have spoken to Foreign Minister Lavrov to call for de-escalation in Crimea and respect for sovereignty and independence of Ukraine," he tweeted.

Hague said he would travel to Ukraine on Sunday to hold talks with the new leadership after Prime Minister David Cameron told Russia to respect the volatile nation's territorial integrity.

Cameron spoke to Russian President Vladimir Putin on Friday.