KHARTSYZK, Ukraine — Howitzers were moving away from the largest rebel-held city in eastern Ukraine, heading further into separatist-controlled territory, and the rebels said they have begun a large-scale pullback of heavy weapons in line with an international peace plan. That plan aims to form a wide buffer zone between separatists' and Ukrainian forces' artillery. The pullback claim by Eduard Basurin, a top commander for rebels in the Donetsk region, couldn't immediately be confirmed. Michael Bociurkiw, a spokesman for the observer mission that is monitoring the fighting in eastern Ukraine, said he couldn't comment until receiving monitors' reports at the end of the day. Rebels in the neighboring separatist Luhansk region also said a pullback was taking place. But Associated Press journalists saw about a dozen howitzers moving from Donetsk city through the town of Khartsyzk, about 10 kilometers (six miles) east of the line of conflict. Their final destination was unclear. The peace plan that was signed Feb. 15 calls for heavy weapons to be pulled back by each side from the front line by 25 to 70 kilometers (15 to 45 miles), depending on their caliber. The ceasefire has been troubled by violations, leading to concern that it wouldn't solidify and that fighting would continue. 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 with state television on Monday, said “such an apocalyptic scenario is hardly possible.” A rebel website cited Basurin as saying about 100 122-mm howitzers would be moved on Tuesday. There was no immediate comment from the Ukrainian side, but military officials have said that they won't pull back weapons until a cease-fire fully takes hold. 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 rebels aim to take Mariupol to help establish a land corridor between mainland Russia and the Crimean peninsula that Russia annexed last March. — AP