Worst shelling in a month as both sides flout cease-fire in Ukraine

East Ukraine’s rebel stronghold Donetsk was pummeled on Sunday by the heaviest shelling in a month, the same day the Organization for Security and Co-operation in Europe (OSCE) reportedly spotted an armored column of troops without insignia in rebel territory that Kiev said proved Moscow had sent reinforcements.

The two-month-old cease-fire to end the war between the government in Kiev and Russia-backed separatists in Ukraine’s east has appeared shakier than ever in the past few days, with both sides accusing the other of violating the terms of the peace plan. Since February, 4,000 people have been killed in the fighting.

Witnesses said the shelling in Donetsk on Sunday sounded more intense than at any time since early October, when a playground was struck killing at least 10 people. The latest strikes appeared to come from territory held by both government and rebel forces.

Ukraine's military said its standoff with the separatists had intensified in the past week, as the rebels swore in new leaders after independent elections the government argues were held in violation of the terms of the truce pact.

Ukraine has accused Russia of sending a column of 32 tanks and truckloads of troops into the country's east to support the pro-Russian rebels in recent days. Moscow has long denied its troops operate in east Ukraine, although many have died there.

The OSCE, which includes Russia and Ukraine as well as the United States and NATO countries, operates in east Ukraine with the blessing of all sides and is widely seen as neutral.

Its statement that it spotted an unidentified armored column in rebel territory helps support Kiev's position that Moscow has been sending in reinforcements to protect separatist enclaves the Kremlin now refers to as "New Russia."

In one 40-vehicle convoy, "19 were large trucks – Kamaz type, covered, and without markings or number plates – each towing a 122mm howitzer and containing personnel in dark green uniforms without insignia," the OSCE said in a statement.

Ukraine said it had no doubt the new troops were Russians.

"Although the OSCE did not specify to whom the equipment and soldiers belonged, the Ukrainian military has no doubt of their identity," said military spokesman Andriy Lysenko. He said Ukraine's military believes Russia might stir up tension to provide grounds to "send in so-called Russian peace-keeping units," which Kiev fears could serve as an invading force.

In rebel-held Donetsk, intense shelling by heavy artillery continued throughout the night and into the early hours, and then picked up again later on Sunday morning. The shelling could be heard in the center of the city, which had a pre-conflict population of more than 1 million.

Large clouds of black smoke could be seen over the ruins of the airport, which is still under government control but which the separatists are seeking to seize.

There were no immediate reports of new civilian casualties. Lysenko said three Ukrainian soldiers had been killed in the past 24 hours and a further 13 injured.

OSCE Chairman Didier Burkhalter said Saturday he was "very concerned about a resurgence of violence in the eastern regions of Ukraine and about activities leading to more fragility instead of further stabilization of the situation."

He urged both sides to stick to the agreements reached in a 12-point cease-fire deal on Sept. 5.

The United States and European Union have imposed economic sanctions on Moscow over Ukraine since March, when Russia seized Ukraine's Crimea peninsula. Moscow has since backed separatists who rose up in east Ukraine, while denying the presence of its own troops.

The sanctions have hurt Russia's economy, already facing a fall in the price for its oil exports, and have helped drive a crash in the value of the Russian ruble.

U.S. Secretary of State John Kerry said on Saturday the United States and Russia had agreed to exchange information about the situation on the Russia-Ukraine border due to some "some disagreements about some of the facts on the ground."

Although Russia blames the crisis on Kiev and the West, NATO said it has overwhelming evidence that Russia has aided the rebels militarily in the conflict.

Al Jazeera and Reuters