The United States will expand military cooperation with Poland and Baltic states to show "support" for its allies after Russia's intervention in Ukraine, Pentagon chief Chuck Hagel said Wednesday.

The moves to expand aviation training in Poland and step up the U.S. role in NATO's air patrols over Baltic countries were clearly designed to reassure alliance partners in Central and Eastern Europe who are alarmed over Russia's actions in the Crimean peninsula.

British Foreign Secretary William Hague has urged his Russian counterpart to de-escalate the situation in Ukraine's restive Crimea peninsula, ahead of a trip to Kiev on Sunday.

"Have spoken to Foreign Minister (Sergei) Lavrov to call for de-escalation in Crimea and respect for sovereignty and independence of Ukraine," Hague said in a Twitter message on Saturday.

Polish Foreign Minister Radoslaw Sikorski cut short a visit to Iran on Saturday to handle the deepening crisis in Crimea after pro-Russian gunmen seized the government and parliament buildings.

"I have to shorten my visit to Iran due to the developments in Crimea and return to Poland," Sikorski told a joint news conference with his Iranian counterpart Mohammad Javad Zarif.

Germany, France and Poland said they were "deeply concerned" Friday over developments on the volatile Crimea peninsula and called for everything to be done to reduce tensions in Ukraine.

"Everything must be done in order to reduce the tensions in the eastern regions of the country and to promote a peaceful dialogue between all participating powers," the three EU countries' foreign ministers said in a joint statement.

Anxious Western powers voiced fear over the growing Crimea crisis Thursday, warning Russia not to escalate tensions and telling pro-Moscow separatists they were playing a "dangerous game."

After dozens of pro-Russian gunmen seized government buildings in the volatile peninsula -- raising fears of a full-blown regional conflict -- NATO leader Anders Fogh Rasmussen tweeted his concern and pleaded with Moscow "not to take any action that can escalate tension or create misunderstanding."

The dramatic events in Kiev on Saturday do not amount to a coup, Polish Foreign Minister Radoslaw Sikorski said, after the Ukrainian president accused the emboldened opposition of a coup d'etat as it asserted control in the capital.

"No coup in Kiev. (Government) buildings got abandoned," Sikorski tweeted, adding that Ukrainian President Viktor Yanukovych has 24 hours to sign into law constitutional reforms agreed under a peace deal on Friday, which Poland helped broker.

Poland's foreign minister said Friday he had received signals in Kiev that the Ukrainian president was prepared to use force should the opposition have rejected an EU brokered roadmap to end a bloody crisis.

"We were getting signals that in case the agreement fails, President (Viktor) Yanukovych was preparing to use Interior Ministry forces," Foreign Minister Radoslaw Sikorski told reporters in Warsaw Friday evening after returning from Kiev.

Talks led by three EU ministers on the future of Ukraine have stopped the immediate bloodshed, but an agreement remains "far off", Poland's prime minister said Friday.

"For now, this objective (to end bloodshed) has been achieved, but the road to an agreement is still very far off," Prime Minister Donald Tusk told reporters in Warsaw.

The French, German and Polish foreign ministers will be in Ukraine on Thursday after the deadly escalation in the country's political crisis, French Foreign Minister Laurent Fabius said.

Calling for "restoring political dialogue between the opposition and the government," Fabius said he, German Foreign Minister Frank-Walter Steinmeier and Poland's Radoslaw Sikorski would hold meetings in Ukraine early Thursday before emergency talks among EU ministers in Brussels.

Those responsible for acts of violence and abductions in Ukraine must be identified and held accountable, Poland's premier Donald Tusk and European Commission chief Jose Manuel Barroso said Thursday.

During a joint and brief news conference held after talks on the crisis in Ukraine, the Polish premier also warned that there could be no European Union assistance to Kiev until the authorities called a halt to the violence.