Ukraine Says Russian Forces Lead Major New Offensive in East

NOVOAZOVSK, Ukraine — Tanks, artillery and infantry have crossed from Russia into an unbreached part of eastern Ukraine in recent days, attacking Ukrainian forces and causing panic and wholesale retreat not only in this small border town but also a wide section of territory, in what Ukrainian and Western military officials described on Wednesday as a stealth invasion.

The attacks outside this city and in an area to the north essentially have opened a new, third front in the war in eastern Ukraine between government forces and pro-Russian separatists, along with the fighting outside the cities of Donetsk and Luhansk.

Exhausted, filthy and dismayed, Ukrainian soldiers staggering out of Novoazovsk for safer territory said Tuesday they were cannon fodder for the forces coming from Russia. As they spoke, tank shells whistled in from the east and exploded nearby.

 Some of the retreating Ukrainian soldiers appeared unwilling to fight. The commander of their unit, part of the Ninth Brigade from Vinnytsia, in western Ukraine, barked at the men to turn around, to no effect. “All right,” the commander said. “Anybody who refuses to fight, sit apart from the others.” Eleven men did, while the others returned to the city.

Some troops were in a full, chaotic retreat: a city-busload of them careened past on the highway headed west, purple curtains flapping through windows shot out by gunfire. A Ukrainian military spokesman said Wednesday the army still controlled Novoazvosk but that 13 soldiers had died in the fighting.

The behavior of the Ukrainian forces corroborated assertions by Western and Ukrainian officials that Russia, despite its strenuous denials, is orchestrating a new counteroffensive to help the besieged separatists of the Donetsk People’s Republic, who have been reeling from aggressive Ukrainian military advances in recent weeks.

“Russia is clearly trying to put its finger on the scale to tip things back in favor of its proxies,” said a senior American official. “Artillery barrages and other Russian military actions have taken their toll on the Ukrainian military.”

The Obama administration, which has placed increasingly punitive economic sanctions on Russia because of the Ukraine crisis, asserted over the past few days that the Russians had sent new columns of tanks and armor across the border.

“These incursions indicate a Russian-directed counteroffensive is likely underway,” Jen Psaki, the State Department spokeswoman, said Wednesday. At the department’s daily briefing in Washington, Ms. Psaki also criticized what she called the Russian government’s “unwillingness to tell the truth” that its military had sent soldiers as deep as 30 miles inside Ukraine territory.

Ms. Psaki apparently was referring to videos of captured Russian soldiers, distributed by Ukraine’s government on Tuesday, that directly challenged President Vladimir V. Putin’s assertions that Russia is a mere bystander in the conflict. The videos were publicized just as Mr. Putin was meeting with his Ukraine counterpart, Petro O. Poroshenko, in Belarus.

Russian forces have been trying to help the separatists break the siege of Luhansk and have been fighting to open a corridor to Donetsk from the Ukrainian-Russian border, Western officials say.

To the south, Russia has been backing a separatist push toward the southern town of Mariupol, a major port on the Sea of Azov, according to Western and Ukrainian officials. The Russian aim, one Western official said, is to open a new front that would divert Ukrainian forces from Donetsk and Luhansk and to possibly seize an outlet to the sea in the event that Russia tries to establish a separatist enclave in eastern Ukraine.

Some Western officials fear the move might even be a step in what they suspect is a broader Russian strategy to carve out a land link to Crimea, the strategic Ukrainian peninsula that Russia annexed in March, setting off Moscow’s worst crisis with the West since the Cold War.

The Russian military’s use of artillery from locations within Ukraine is of special concern to Western military officials, who say Russian artillery has already been used to shell Ukrainian forces near Luhansk. And along with the antiaircraft systems operated by separatists or Russian forces inside Ukraine, the artillery has the potential to alter the balance of power in the struggle for control of eastern Ukraine.

Russia has denied that it has intervened militarily in Ukraine and the separatists have asserted that they are using captured Ukrainian equipment. But American officials say they are confident that the artillery in Ukraine’s Krasnodon area is Russia’s since Ukrainian forces have not penetrated that deeply into that separatist-controlled region. American officials also say the separatists have no experience in using such weaponry.

“We judge that self-propelled artillery is operated by Russians rather than separatists since no separatist training on this artillery has occurred to date,” an Obama administration official said.

The United States has photographs that show the Russian artillery moved into Ukraine, American officials say. One photo dated Aug. 21, shown to a reporter from The New York Times, shows Russian military units moving self-propelled artillery into Ukraine. Another photo, dated Aug. 23, shows the artillery in firing positions in Ukraine.

Advanced air defenses, including systems not known to be in the Ukrainian arsenal, have also been used to blunt the Ukrainian military’s air power, American officials say. In addition, they said, the Russian military routinely flies drones over Ukraine and shares the intelligence with the separatists.

The Ukrainian retreat from the border area near Novoazovsk, which began on Tuesday, came as Mr. Putin told Mr. Poroshenko that the Ukrainian insurgency an internal matter and that the Ukrainian government needed to negotiate a cease-fire.