MOSCOW — Russia on Sunday accused Ukraine of lobbing a shell over the border and killing a Russian civilian and warned of “irreversible consequences,” in a sharp escalation of rhetoric that raised fears of a Russian invasion in Ukraine’s east.

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

Ukrainian security officials, meanwhile, said that around 100 military vehicles driven by “mercenaries” tried to cross the border from Russia early Sunday, 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. The Russians say it occurred when the Ukrainian army shelled Russia’s Rostov region, hitting a residential building. Two other people were injured, authorities said.

“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.

Russia’s Foreign Ministry said the incident was an “aggressive action” that “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.”

Russian Foreign Minister Sergei Lavrov said last week that his nation was prepared to take all necessary steps to defend its territory – a declaration that appeared to keep open the option of outright intervention in Ukraine. Ukrainian and Western officials have accused Russia of offering quiet support to the rebels, a charge that rebels themselves appeared to confirm this past week, although the extent of the aid is unclear.

Ukrainian officials denied that they fired onto Russian soil, 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,” Andriy Lysenko, a spokesman for Ukraine’s National Security and Defense Council, told a news conference in Kiev 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, he said.

He said 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.” Ukrainian artillery fired on them, he said. Ukrainian officials said they were still working to determine further details about the incident.