Howitzers were seen moving east Tuesday from the largest rebel-held city in eastern Ukraine further into separatist-controlled territory, but the Ukrainian government disputed the rebels' claim that a heavy weapons pullback had begun.

A peace plan worked out in marathon talks on Feb. 12 aims to create a wide buffer zone between separatists' and Ukrainian forces' artillery as part of efforts to end the conflict that has left nearly 5,800 dead since April.

The disagreement over a weapons pullback came as talks about a fragile peace deal for Ukraine were underway in Paris between the foreign ministers of Russia, Ukraine, Germany and France.

While Eduard Basurin, a top commander for rebels in the Donetsk region, said his side had begun a large-scale pullback of heavy weapons in line with the peace plan, the claim could not be verified. A rebel website quoted him as saying 100 122-mm howitzers would be involved.

Michael Bociurkiw, a spokesman for the international team monitoring the fighting, said he couldn't comment until receiving monitors' reports at the end of the day. The Ukrainian military dismissed the rebel pullback claim and said its forces would not draw their weapons away until a cease-fire takes hold.

A rebel official in the separatist Luhansk region claimed that Ukrainian forces had begun a partial pullback themselves, but Ukrainian military spokesman Col. Andriy Lysenko said no Ukrainian moves were underway.

The rebels "are just regrouping their gangs and are relocating their weapons," he told reporters. "As soon as there is a cease-fire for two days, that is the signal to start a withdrawal."

Associated Press journalists saw about a dozen howitzers moving from the rebel-held city of Donetsk through the town of Khartsyzk, six miles east of the line of conflict. Their final destination was unclear.

The peace plan calls for heavy weapons to be pulled back 15 to 45 miles from the front line, depending on their caliber.

The supposed cease-fire in eastern Ukraine has been troubled by violations. On Tuesday, military spokesman Lt. Col. Anatoliy Stelmakh said rebels had shelled the town of Popasna seven times and launched one barrage on the village of Luhanske.

Stelmakh also said rebels tried to storm Ukrainian positions near the southern village of Shyrokyne, which is near the strategic Azov Sea port of Mariupol. Concerns persists that the rebels aim to take Mariupol to help establish a land corridor between mainland Russia and the Crimean Peninsula, which Russia annexed last March.

Russia denies Ukrainian and Western claims that it is supplying the rebels with troops and equipment, with the possible aim of a full-scale war. Russian President Vladimir Putin, in an interview Monday with state television, said "such an apocalyptic scenario is hardly possible."

Western officials and NATO insist, however, that satellite photos show that Russian military equipment is in eastern Ukraine.