Fighting continued in eastern Ukraine on Monday, as a new round of talks were due to start in Minsk, Belarus, aimed at ending the crisis, which for the first time would include representatives of the Russia-backed separatist movement.

The Ukrainian military spokesman, Andriy Lysenko, said Kiev's forces had abandoned the airport in Luhansk after it came under attack by a Russian tank battalion. There were also reports of fighting at Donetsk airport, while the Ukrainian army and volunteer battalions reported heavy casualties in recent days as they attempt to retreat from encirclement in the town of Ilovaisk.

In Minsk, a week after talks between the Russian and Ukrainian presidents, a "contact group" was due to meet, apparently including former Ukrainian president Leonid Kuchma and Andrei Purgin, a Donetsk rebel leader.

The rebels have previously declared themselves independent statelets, but Russian agencies reported on Monday that in Minsk they were putting forward a range of demands on regional self-determination and Russian language status that would apparently keep the regions inside Ukraine.

Kiev is unlikely to agree to give into demands from the rebel leaders, but the change of tone shows that having boosted the rebels militarily, Moscow may be looking for a compromise solution that still gives it sway over swaths of Ukraine. Even if the sides did agree, it is unclear whether all the units fighting on both sides would accept a compromise.

President Vladimir Putin said on Sunday that talks should begin on statehood for south-eastern regions, but his spokesman later clarified that the Russian president was apparently only talking about increased status within Ukraine. Putin again called for an immediate ceasefire.

Kiev has drawn up a peace plan but wants to win militarily against the armed separatists and only then offer broad concessions for the Russian-speaking people of the east. However, the Ukrainian military offensive has led to hundreds of civilian casualties as both sides use heavy artillery.

Kiev appeared to be making gains in recent weeks before what looked like a boost from Russian forces to aid the rebels and retain the balance of power on the ground.

At the first day of classes at Russia's leading diplomatic university, the Moscow State Institute of International Relations, the foreign minister, Sergei Lavrov, used his address to students to insist that "there would be no military intervention" in Ukraine by Russia.

His remarks defy mounting evidence that Russian forces are active in Ukraine. The foreign minister called for "an exclusively peaceful settlement of this severe crisis, this tragedy". Putin has also demanded an immediate ceasefire, which would give the rebels in Donetsk and Luhansk regions a platform to win concessions.

In Mariupol, a major port city on Ukraine's southern coast, schools opened for the first day of the new term on Monday, as the city braces for a potential assault by rebel forces. Last week rebels, apparently aided by soldiers who appeared to be from the Russian army, seized the town of Novoazovsk further along the coast. They have said they planned to advance on Mariupol, but pro-Kiev residents have been digging trenches on the outskirts of town and promise to defend the city.

"I don't care if we are part of Russia, part of Ukraine or part of Mars," said Irina Filatova, as she took her daughters to school. "The main thing is that we can live in peace and all of this can finish."

In the rebel strongholds of Donetsk and Luhansk, the vast majority of schools did not open due to the chaotic situation, with regular shelling and shortages of water and electricity having created a humanitarian crisis in recent weeks.