DONETSK, Ukraine — Further muddying the prospects for a diplomatic breakthrough, government officials in Kiev accused Russia on Monday of opening a new front in the war by sending an armored column across the border south of the Ukrainian lines that surround the rebel capital, Donetsk.
The Russian government dismissed the accusation, and Foreign Minister Sergey Lavrov, speaking in Moscow, said Western governments should not expect his country to make all of the concessions in a settlement, and Ukraine, too, would have to compromise.
The Ukrainian military said 10 tanks, two armored infantry vehicles, and two trucks operated by Russian soldiers disguised as separatist fighters had crossed the border near the town of Novoazovsk and engaged in combat with Ukrainian border guards. The statement could not be independently confirmed.
Andriy Lysenko, a Ukrainian military spokesman, said Russian military vehicles flying separatist flags ‘‘violated the state border of Ukraine’’ and advanced on a road to Mariupol. If true, it would be one of the first times that Russia had penetrated Ukraine’s border outside of friendly rebel territory.
Also Monday, Russia announced it would send another convoy of humanitarian aid to eastern Ukraine across a border area controlled by pro-Russia separatists; Ukrainian officials say the movement of goods is calculated to undermine the country’s sovereignty.
In Donetsk on Monday, a bearded gunman wrapped a woman in a Ukrainian flag on a sidewalk and forced her to stand, sobbing in terror, holding a sign identifying her as a spotter for Ukrainian artillery.
“She kills our children,” it read. Because the woman was a spy, said the gunman, a pro-Russia militant, everything that would happen to her would be well-deserved.
Passersby stopped their cars to get out and spit, slap her face and throw tomatoes at her.
This theatrical scene of abuse unfolded a day after the rebel movement paraded Ukrainian prisoners of war on a thoroughfare at bayonet point, then dramatically washed the pavement behind them.
President Vladimir V. Putin of Russia and President Petro O. Poroshenko of Ukraine are slated to meet for peace talks in Minsk, Belarus, on Tuesday.
The taunting and provocation in Donetsk appeared to be aimed at dissuading the Ukrainian government from accepting a settlement that might forestall a broader Russian intervention, a development that separatists here are banking on as their military fortunes wane.
The drama seemed sure to ratchet up tensions. A military unit of Russian nationals from the region of North Ossetia, in southern Russia, held the woman at a checkpoint in a roundabout in Donetsk known as “the Motel,” for a nearby hotel. The men, smiling and gesturing toward the woman, waved to drivers to observe or take part.
“We should hang you on the square,” one woman in the crowd yelled, then walked up and spat in the face of the victim, then kicked her in a thigh, causing the woman accused of spying to stagger back.
The gunmen looked on. At times, the pro-Russia soldiers posed beside the crying woman to take selfies on their smartphones, or twirl her hair with their fingers.
At one point, a fighter walked a few paces back, crouched and aimed a Kalashnikov rifle at the woman in a mock execution. The woman shut her eyes. “Open your eyes, stand up straight!” another of the gunmen yelled.
A member of the Vostok Battalion, which consists of mostly local Ukrainians, said the Ossetian volunteers at the Motel checkpoint do not report to its commanders, so nothing else could be done. He said he condemned the abuse.
At the peace talks in Minsk, Putin and Poroshenko will be joined by representatives of the European Union and the Russia-led Customs Union, including the presidents of Kazakhstan and Belarus.
Although the talks offer some hope for a negotiated settlement, both Putin and Poroshenko are under strong pressure from nationalists at home to press on militarily.
Oleh Voloshyn, a former Ukrainian diplomat, said in a telephone interview from Kiev, the Ukrainian capital, that Poroshenko will use the summit meeting to ask Putin to halt the flow of Russian volunteers and military hardware across the border and may offer, perhaps in private talks or via subordinates on the sidelines, autonomous status for portions of eastern Ukraine in exchange.
The Ukrainian government, however, will not accept any legitimization of the main rebel group, the Donetsk People’s Republic, he said, especially after the public abuse of prisoners.
In Moscow, Lavrov, the foreign minister, was questioned about the parade held Sunday in which prisoners of war from the Ukrainian army were displayed and whether it violated a Geneva Convention prohibition against “outrages upon personal dignity, in particular“humiliating and degrading treatment’’ of POWs.
“I saw a picture of this parade,” Lavrov said. “I did not see anything close to abuse.”