Poland's Prime Minister Donald Tusk warned on Monday that the war in eastern Ukraine risks spreading if NATO does not toughen its stance quickly.

Tusk, tipped as the European Union's next president, claimed that "our Western community is threatened by war, not just in eastern Ukraine", as Poles marked 75 years since the outbreak of World War II.

Ukraine's defense minister warned on Monday that a "great war" had broken out with Russia over his country's future that could claim tens of thousands of lives.

"A great war has arrived at our doorstep -- the likes of which Europe has not seen since World War II. Unfortunately, the losses in such a war will be measured not in the hundreds but thousands and tens of thousands," Valeriy Geletey wrote in a Facebook post.

Representatives of pro-Russian rebels in eastern Ukraine are seeking a special status for the region, a report said Monday, in what would constitute a de facto division of the country.

Spokesmen for the groups based in the eastern cities of Donetsk and Lugansk told Russia's Interfax news agency they were submitting a joint negotiating position in talks being held in Minsk on Monday.

Up to 15,000 Russian soldiers have been sent to Ukraine over the past two months, and at least 200 may have died in combat there, rights groups told AFP on Monday.

Moscow denies that it has deployed regular troops to Ukraine to prop up separatists battling Kiev forces, but multiple indications have emerged over the past weeks that Russian soldiers are on the ground in Ukraine.

Ukrainian forces were forced to retreat from Lugansk airport in the face of a Russian troop attack and Moscow soldiers moved into key cities in the east on Monday, Kiev said, a day after Russian President Vladimir Putin evoked "statehood" discussions for the conflict-torn east.

Putin accused Europe of ignoring the Ukrainian military's "direct targeting" of civilians in the conflict and said the offensive pushed by insurgents there were simply an attempt to expel Kiev's forces from residential areas.

Australia will toughen its sanctions against Russia over the crisis in Ukraine so they match those of the European Union, Prime Minister Tony Abbott said Monday.

Australia already has some sanctions against Russia, but Abbott said these would be tightened as a result of Moscow's persistent and deliberate violation of its neighbor's sovereignty.

The head of the U.S. Senate Foreign Relations Committee called Sunday for supplying Ukraine with weapons to fight what he called a "direct invasion" of the country by Russia.

"We should provide the Ukrainians with the type of defensive weapons that will impose a cost upon (Russian President Vladimir) Putin for further aggression," Robert Menendez told CNN's "State of the Union" talk show.

Russian President Vladimir Putin on Sunday raised the stakes in the Ukraine conflict by calling for the first time for statehood to be discussed for the restive east of the former Soviet state.

The remarks came just hours after the European Union gave Moscow -- which the bloc accuses of direct involvement in the insurgency -- a week to change course or face new sanctions.

Ten Russian paratroopers captured inside Ukraine nearly one week ago have returned home following a troop exchange, Russian media reported Sunday.

In the early hours of Sunday the 10 paratroopers were handed over to Russian authorities at the Nekhoteyevka border crossing.

With pro-Russian rebels threatening at the gates, fighters loyal to Kiev in Mariupol are having to face a hard truth: they will be unable to save this vital port city alone.

"We're the only ones here," sighs “Botsman”, the leader of one unit in the Azov volunteer battalion trying to hold out as pro-Russian rebel forces sweep west.