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MOSCOW— Russia on Sunday accused Ukraine of the cross-border shelling death of a Russian civilian, warning of “irreversible consequences” in a sharp escalation of rhetoric that raised fears in Ukraine of an imminent Russian intervention in the east.

The accusation, which Ukrainian security officials denied, set off furious recriminations in Russia, with one senior legislator calling for pinpoint airstrikes on Ukrainian soil of the sort he said Israel was currently making against the Gaza Strip.

Ukrainian security officials meanwhile said that around 100 military vehicles driven by “mercenaries” had attempted to cross the border from Russia early Sunday morning, and that Ukraine’s military had destroyed some of the vehicles.

Russian officials summoned the Ukrainian charge d’affaires to the foreign ministry in Moscow to protest the civilian’s death, which they say occurred when the Ukrainian army shelled Russia’s Rostov region from across the border, hitting a residential building.

“The only route is to deal with this like a civilized country, like the United States or the European Union. We need to use precision weapons, like Israel’s, to destroy those who launched the bomb,” the deputy speaker of Russia’s upper house of parliament, Yevgeny Bushmin, told the state-run RIA Novosti news service.

“This incident highlights the extremely dangerous escalation of tensions on the Russian-Ukrainian border and may have irreversible consequences, the responsibility for which lies on the Ukrainian side,” Russia’s Foreign Ministry said in a statement Sunday, calling the incident an “aggressive action.”

Ukrainian officials denied that they fired onto Russian territory, saying that the attack may have been the work of provocateurs seeking to draw a Russian reaction.

“Forces of the anti-terrorist mission are not firing on the territory of a neighboring country. Forces of the anti-terrorist mission are not firing on residential areas,” Andriy Lysenko, a spokesman for Ukraine’s National Security and Defense Council, told a news conference in Kyiv on Sunday.

But he told journalists that there had been shelling in the area early Sunday coming from both rebel and Ukrainian army positions. Pro-Russia separatists made a “massive artillery strike” on Ukrainian military forces in Luhansk, just across the border checkpoint from where the shelling death is alleged to have taken place early Sunday, he said. He added that the strike served as cover for “the passage of a major mercenary force into Ukrainian territory” of “around 100 units of armed vehicles and trucks.” Once the column of vehicles was discovered, Ukrainian artillery positions began to fire on them, he said. Ukrainian security officials said they were still working to determine further details about the incident.

It was not immediately possible to confirm either side’s account, nor was it clear why, in the fog of war, Ukrainian officials could be certain that a stray shell had not hit the Russian side nor why Russian officials could be sure that the shell was indeed Ukrainian. Rebels and Ukrainian military forces possess heavy artillery and tanks.

The Ukrainian Foreign Ministry said Sunday that Ukraine was “ready to cooperate” in any Russian investigation of the incident, and it said in a statement that it “expressed regret at the deaths and injuries” of the Russian citizens.

Ukraine has struggled to maintain control of its porous border, and separatists have taken over several border checkpoints. Ukrainian officials say that the Russian government has tolerated the passage of a steady stream of military equipment and volunteers over the border to fight, a charge that Russia has denied.

Russia has been registering increasingly strong complaints that its border crossings and territory are being shelled from the Ukrainian side, although Sunday was the first time that it said that anyone had died as a result. Last weekend, Russia said a group of investigators and a customs checkpoint had been fired on. On Saturday, Russia said a cross-border attack also hit a Russian border patrol in the Rostov region, damaging a vehicle.

Russian President Vladimir Putin on Sunday said that “incidents where shells reach Russian territory, leading to today’s tragedy in the Rostov region, are unacceptable,” Kremlin spokesman Dmitry Peskov told reporters in Rio de Janeiro on Sunday after Putin met with German Chancellor Angela Merkel, the Interfax news agency reported. The two leaders were in Brazil to watch the World Cup final, and they met beforehand to discuss the situation in Ukraine.

“Continued practice of this kind is absolutely unacceptable,” Peskov described Putin as saying.

Rebels made a significant retreat on July 5, pulling back from the cities of Slovyansk and Kramatorsk and fortifying themselves inside the far larger city of Donetsk. Since then, Ukrainian military forces have struggled to extend their gains, although fierce fighting has taken place around Ukraine’s east, including a single incident in which 19 Ukrainian soldiers were killed when they were hit in a massive rocket attack.

Russia has not responded to direct appeals for aid from the rebels since the retreat. But Russian Deputy Foreign Minister Grigory Karasin said Sunday that the incident “will not be left without a reaction.” He called for “an immediate end to the bloodshed” in Ukraine.

Birnbaum reported from Dnepropetrovsk, Ukraine.