KIEV/VIENNA - Ukraine would be ready for a new round of Geneva negotiation to ease its tension if Russia supports its presidential election, Ukraine's acting foreign minister said in Vienna on Tuesday.

"If Russia is ready to commit itself to supporting these elections and to eliminate this threat and eliminate its support for the extremist elements in Ukraine, we are ready to have such a round of meetings," Andrii Deshchytsia told reporters during a meeting of the Council of Europe in Vienna with focus on the Ukraine crisis.

Ukraine's presidential election process is the short-term priority of the country, he said, adding that the election is scheduled for May 25.

He made the remarks shortly after Russian Foreign Minister Sergey Lavrov said it would be "unusual" to hold a presidential election in Ukraine while the government was deploying the army against "some of its people."

Lavrov also said the new round of international negotiation on de-escalating the tension in Ukraine should include the "opposition" on the negotiation table, an opinion rejected by Ukraine later.

At Donetsk Airport in eastern Ukraine, outgoing and incoming flights have been canceled until further notice, the airport's press service said Tuesday.

The suspension came after government troops launched an "anti-terror" operation against pro-Russia militants in Slavyansk to retake the city, located 115 km north of Donetsk, which has been under the control of pro-Russian activists since unrest began in eastern Ukraine.

At least four Ukrainian servicemen were killed and some 30 wounded during the operation, the Interior Ministry said.

Meanwhile, Ukraine sent a special force unit to the southern port of Odessa Monday to replace local police who had, according to Ukraine's Interior Ministry, failed to tackle rebel actions at the weekend.

The dispatch was seen as a signal that Kiev fears the situation in Odessa would escalate to a broader civil war while tackling rebellion in the east.

The loss of Odessa would be catastrophic for the new government in Kiev as it will leave the country cut off from the Black Sea. Ukraine lost a significant part of its coastline in March, when its Crimean Peninsula voted to join Russia.

Also on Tuesday, the United States and the European Union agreed to impose more sanctions on Russia in response to what they called its "destabilization" moves in eastern Ukraine.

Russia has denied the accusation, and called instead for the Ukrainian troops to be withdrawn and a dialogue between the Kiev government and the militants.

The United States and the EU, however, urged Russia to live up to its commitments made in Geneva on April 17 in a meeting with the US, the EU and Ukraine, which include using its influence over the militants to get them to disarm and engage peacefully in Ukraine's political process.

The United States also rejected the efforts of pro-Russia separatists in eastern Ukraine to organize a "contrived and bogus" independence referendum on May 11.

Germany warned that Ukraine was close to a military confrontation and more efforts were needed to be made to prevent a new Cold War.

"The bloody pictures from Odessa have shown us that we are just a few steps away from a military confrontation... The Ukraine conflict has increased in speed and intensity, in a way we would not have thought possible some time ago," German Foreign Minister Frank-Walter Steinmeier said.

Meanwhile, energy ministers from the G7 group of leading world economies agreed Tuesday to help Ukraine after Russia threatened to halt gas supplies over unpaid bills in a move that could create havoc in Europe.