KYIV, Ukraine -- Both government troops and pro-Russian rebels began withdrawing heavy artillery in the east of the country, Ukrainian officials said Monday, a significant step toward implementing an effective cease-fire in the region.

Col. Andriy Lysenko, spokesman for Ukraine's National Security and Defence Council, said Kyiv's forces had started withdrawing from frontline positions. He said the rebels had also begun their withdrawal of heavy artillery, although it was "not as massive as we expected."

"We are seeing a trend that (the rebels) are reducing their use of heavy armed weaponry," Lysenko told journalists in Kyiv. He said neither Kyiv nor the rebels had completed their withdrawals, but said he hoped the rebels "will follow the example of the Ukrainian servicemen."

A cease-fire imposed Sept. 5 has been riddled by violations from the start, adding civilian casualties to the estimated 3,000 people who have been killed since the conflict began in April.

On Monday, explosions were heard in the north of the rebel-held city of Donetsk, where fighting in recent weeks centred on a government-held airport has caught many residential areas in the crossfire. Later, smoke rose over a neighbourhood in that area and rebels blocked an Associated Press photographer from travelling there.

Lysenko said two Ukrainian servicemen had been killed in the past day.

Ukraine, Russia and the Moscow-backed rebels last week signed an agreement to further the peace process by halting advances and pull back heavy artillery, creating a buffer zone between them.

The deal, supported by the Organization for Security and Cooperation in Europe, also specifically bans flights by combat aircraft over the area of conflict and setting up new minefields.

It could be a significant step forward in finally bringing an end to the simmering conflict, although negotiators have not yet addressed the future status of the rebel regions, the most politically controversial issue.

In an interview with Ukrainian news channels released late on Sunday, Ukrainian President Petro Poroshenko pleaded with the public to give the peace deal time to work.

"Solving the war in Luhansk and Donetsk with military alone is impossible," he said. "The more military groups we have there, the more the Russian army will send."

Poroshenko said that 65 per cent of military equipment deployed by Kyiv in the east has been destroyed. During a trip to the United States last week, the Ukrainian president pleaded for lethal weapons for his country's army. The U.S. gave Poroshenko $46 million in security aid, but excluded lethal weapons from the deal.

Poland's Defence Minister Tomasz Siemoniak on Monday confirmed that Poland is ready to sell arms to Ukraine.

"Since July, there is no embargo on arms sale to Ukraine," he said in an interview with the radio station Zet, adding that Poland and "many other countries" are prepared to offer their products.

Siemoniak said that Ukraine is now getting acquainted with the list of armaments made in Poland, but that the two countries have agreed not to discuss the details publicly.

- Monika Scislowska in Warsaw, Poland, and Darko Vojinovic in Donetsk, Ukraine contributed reporting.