Ukraine reported more deaths among its troops and separatists on Sunday despite a ceasefire, but President Petro Poroshenko defended his peace plan, saying a military solution was no option and Western support could have been at risk.

The Kyiv military accused separatists and Russian troops of violating the Sept. 5 ceasefire in eastern Ukraine by continuing to shoot at government forces. Kiev would not go ahead with setting up a proposed buffer zone until the violations stopped.

"In the last 24 hours we have lost two Ukrainian soldiers, eight have been wounded," military spokesman Andriy Lysenko told reporters on Sunday.

Lysenko said separatists had carried out a further attack on the government-held international airport of Donetsk, the east's main industrial hub. The rebels hold the city of Donetsk.

He said 40 separatist fighters had been killed in "defensive" fire by Ukrainian forces. There was no independent confirmation of this figure.

Poroshenko declared the ceasefire after considerable battlefield losses against the separatists which Kiev ascribed to direct military intervention by Russian troops. Moscow denies its forces are involved in the conflict, in which more than 3,000 people have been killed, despite what Kyiv and Western governments say is undeniable proof.

The Ukrainian leader, in a televised question-and-answer session with a group of Ukrainian journalists after returning from the United States, acknowledged that Ukrainian troops were still being killed but he said the death rate was "ten times fewer" than before.

"It's not possible to win … purely by military means. The more Ukrainian army battalions or brigades are brought up, the more troops there are from the Russian Federation," he said, adding that 60-65 per cent of Ukraine's military equipment on the front-line had been destroyed.

And Ukraine would not win without international support, he added, suggesting he had been under pressure from the U.S. and other Western governments to declare a ceasefire and work for a political compromise.

Under attack

Poroshenko has come under attack from within the pro-Western establishment at home for laws, bull-dozed through parliament, which grant "special status" to independence-minded separatists who have declared "people's republics" in the east and would allow them to enjoy limited self-rule for a three-year period.

The plan, which would also grant freedom from prosecution to separatists who have been fighting government forces, has also been met with derision by rebels who say they do not want to be part of Ukraine.

A Reuters correspondent in Donetsk said Sunday's exchange, in which the Ukrainian side also handed over 28 separatist fighters, took place about 20 kilometres outside Donetsk with the sound of artillery firing from the airport in the background.

Poroshenko said priorities were to get all Russian troops, which have already been withdrawing, out of the country. "We'll monitor this. We'll say when the last Russian soldier has left," he said adding the border with Russia had to be closed as well.

Ukraine destruction

A firefighter sprays water on a damaged office building after shelling in the town of Donetsk, eastern Ukraine, on Sunday. ( Darko Vojinovic/The Associated Press)

Poroshenko addressed the U.S. Congress and met President Barack Obama during a trip to Washington on Thursday which brought Ukraine $53 million US in fresh aid, though no promise of lethal weaponry.

The Ukrainian leader said on Sunday that though Ukraine had machine-guns, tanks, missile systems, rockets and artillery it expected to receive intelligence equipment, radar and observation systems that "will allow us to increase ten-fold the effectiveness of our weapons."

The Ukrainian military's more downbeat assessment of the situation echoed that of NATO's top military commander, U.S. Air Force Gen. Philip Breedlove, who said on Saturday that fighting was continuing in Ukraine and that the truce was a ceasefire "in name only."

"The situation in Ukraine is not good right now," Breedlove told reporters in the Lithuanian capital of Vilnius following a meeting of chiefs of defence of NATO countries. "Basically, we have a ceasefire in name only."

Ukraine's warring sides agreed on Friday to withdraw artillery and other heavy weapons to the outer limits of a 30 kilometre buffer zone, building on the ceasefire. But the military spokesman, Lysenko, said work on establishing the buffer zone could not start while the ceasefire was being violated.

Russians protest

Earlier Sunday, tens of thousands of people marched through central Moscow to protest the fighting in Ukraine and Russia's alleged complicity in the conflict. An Associated Press reporter estimated the crowd at about 20,000, although the city police department put the number at about 5,000.

The demonstrators chanted slogans including "No to war" and "The junta is in the Kremlin, not Kyiv." The latter refers to Russia's contention that the ousting of Ukraine's former Russia-friendly president was a coup.

"Our country is acting as an aggressor, like Germany in the war," said demonstrator Konstantin Alexeyev, 35.

"I am concerned about the rhetoric on our TV channels, which disseminate anti-Ukrainian sentiment," said Ludmila Shteigervalt, 50. "Ukraine is a friendly country. We should just leave it alone."

At least one scuffle broke out between protesters and nationalists who unfurled a banner denouncing "The March of Traitors."

With files from The Associated Press