Moscow: Moscow on Sunday warned Kiev of "irreversible consequences" after a man was killed by a shell in a Russian border town in what it branded as Ukrainian aggression.
"The Russian side views the provocation as another act of aggression by Ukraine toward sovereign Russian territory and citizens of the Russian Federation," the Russian foreign ministry said in a statement.
"The incident shows extremely dangerous escalation of tensions at the Russian-Ukraine border and can have irreversible consequences, for which Ukraine will bear responsibility," it said.
Ukraine denied firing at Russian territory. "Ukrainian troops are definitely not shooting at Russia," said Andriy Lysenko, a spokesman for Ukraine`s national security and defence council. "We did not shoot," he said.
Several "explosive shells" killed one Russian and "seriously injured" two more, the Russian ministry said.
A protest note was given to Ukraine`s charge d`affaires in Moscow, it said. Kiev had recalled its ambassador in March over Moscow`s annexation of Ukraine`s Crimea peninsula in the Black Sea.
Rostov regional authorities spokesman Alexander Titov told Russian agencies earlier that shells fired from Ukrainian territory killed a local man and injured an elderly woman in a small Russian border town of Donetsk.
"Around 9:20 am (0520 GMT) a shell flew on the territory of Donetsk from Ukrainian territory. Two residential houses were damaged, one person died," Titov told Russian agencies.
Russian investigators said they launched a probe to investigate the "murder".
Deputy Foreign Minister Grigory Karasin said the incident represented a "dangerous escalation for our citizens" and vowed it "will clearly not be left without a response," in televised remarks.
The small Russian town of Donetsk is near the border with Ukraine`s Lugansk region, where Kiev-backed troops and pro-Russian separatists are fighting for the control of border checkpoints.
On Saturday the Russian foreign ministry warned Ukraine over what it said were continued attacks on its territory during the conflict, adding that it "has the right to take measures to protect its territory and ensure the security of Russian citizens".