Battle rages between Russian-backed rebels and Ukraine military

Shelling from both Ukrainian military and rebel separatist positions continued Wednesday over a remote border checkpoint northwest of Luhansk that Ukraine said was seized Monday by Russian troops, a chief spokesman for the Ukrainian military said.

With President Petro O. Poroshenko of Ukraine claiming that thousands of additional Russian troops had crossed into Ukraine and engaged directly with Ukrainian forces, attention has shifted from the battle over the battered airport at Donetsk to this fresh front on the main road to the city of Luhansk, 90 miles northeast of Donetsk.

Lt. Col. Roman Turovets, a Ukrainian spokesman at the base here, the main one in the conflict area, said that Ukraine believed the soldiers it was engaging near the town of Krymske, northwest of Luhansk, were highly trained Russian regulars, based on their tactics, their weaponry and on intelligence.

Checkpoint 31, on an access road into Luhansk, had been bombarded by shelling for most of Tuesday, Colonel Turovets said. Then late in the afternoon darkness, and under cover of heavy fog, the suspected Russian forces were able to drive away the Ukrainians, who suffered no casualties.

In response, Ukraine shelled the position and there was an exchange of fire that continued through Wednesday.

Russia, as it has since the conflict started last year, denied any involvement in the Ukraine fighting others than the possible participation of Russian “volunteers” wishing to aid the separatists. The foreign minister, Sergey Lavrov, challenged Ukraine to “present the proof” if Russian troops were really in Ukraine.

“The people who attacked, they were very professional,” said Colonel Turovets, the Ukrainian spokesman. “Our troops could tell they were well-trained, from how they moved.”

In Berlin on Wednesday, Mr. Lavrov and the foreign ministers of Ukraine, France and Germany met for about three hours to try to shore up thecrumbling cease-fire in the east. After the meeting, a joint statement called on the combatants to “cease hostilities and withdraw heavy weapons.” Russia has proposed that both the separatists and the Ukrainian Army withdraw heavy weaponry from a buffer zone along the front line, to defuse the tension. Ukrainian officials have rejected this proposal, saying it is Russia that has been sending artillery and other arms into the area.

The United States ambassador to the United Nations, Samantha Power, accused Russia of training, equipping and fighting with the separatist rebels, even as the Kremlin proposed a peace plan. “Let us pull the veil away from Putin’s peace plan and call it for what it is — a Russian occupation plan,” she said at a Security Council meeting on Ukraine.

The Russian ambassador, Vitaly I. Churkin, accused Ukraine of repeatedly violating the cease-fire agreement, reached in Minsk, Belarus, last year. In eastern Ukraine, an Associated Press reporter on Wednesday saw pro-Russian rebels driving six self-propelled howitzers, four Grad rocket launchers and 15 tanks toward the front and the battle for Checkpoint 31. The tanks were described as in pristine condition.

Also on Wednesday, separatists blew up a bridge near the battle for Checkpoint 31, adding to the dozens of bridges already destroyed by both sides in the swirl of retreats and feints over nine months of fighting.

On Tuesday, a strategic railroad bridge was blown up in the Zaporozhye region, far from the front lines, halting at least temporarily shipments of iron ore to steel mills in the port of Mariupol.

At the World Economic Forum in the Swiss ski resort of Davos, Mr. Poroshenko said he would cut short his visit to help oversee the combat in the east. In a speech, Mr. Poroshenko held up a dented, shrapnel-pocked panel of a public bus in which 13 people died from a rebel rocket strike, trying to drive home to European businessmen, who have grumbled about Western sanctions, the human cost of the war.

Mr. Poroshenko said 9,000 Russian troops were fighting on Ukrainian soil.

“If this is not aggression, what is?” he said.

Ukraine also on Wednesday began enforcing a new set of strict rules for crossing between territory controlled by the government in Kiev and territory controlled by the separatists in eastern Ukraine. Only people holding new passes issued by the Ukrainian government would be allowed to pass through any of the seven main crossing points, and those trying to get across on secondary roads would be regarded as in violation of Ukrainian military rules, Colonel Turovets said.

Only a handful of police stations just outside the conflict zone would handle applications, and the passes would require a 10-day wait. Only civilians with a clear reason for crossing the border would be given the passes.

The effect would be to seal up the border in the coming days, if the new rules are enforced, but would do nothing to shore up the porous border with Russia.

“What people don’t always realize is that there are several hundred kilometers of border with Russia that is not controlled,” Colonel Turovets said, allowing Russian drug smugglers and potential terrorists to come into Ukraine. “So that is why we put tougher conditions on this line,” he said.

If that caused more hardship for civilians inside the conflict zone, that was the fault of the Russians, he said.

“Everybody understands if there were no Russian mercenaries in Ukraine then this war would have been over long ago,” he said.

NY Times