MOSCOW -- Russia's foreign ministry said Sunday that a Ukrainian shell hit a town on the Russian border, killing one person and seriously injuring two others. But Ukraine denied firing a shell into Russian territory.

A statement from Russia's foreign ministry labeled the incident a "provocation," and warned of the possibility of "irreversible consequences, the responsibility for which lies on the Ukrainian side."

Russia says the shell hit the courtyard of a residential building in the Russian town of Donetsk early on Sunday. The town borders Ukraine's restless east, where a pro-Russian separatist insurgency has waged a three-month long battle with the Kyiv government.

Ukrainian officials denied that any Ukrainian shells had fallen on Russian territory. Andriy Lysenko, a spokesman for Ukraine's National Security and Defence Council, was quoted by Interfax as saying that Ukrainian forces "do not fire on the territory of a neighbouring country. They do not fire on residential areas." He placed blame for the attack on the rebels themselves, and condemned the shelling as a "provocation."

Russia has made repeated claims that settlements along its porous border with Ukraine -- which the West and Kyiv say is a key supply route for the rebels -- have been hit by Ukrainian fire, but no deaths have been previously reported.

The claims come as President Vladimir Putin, whose nation will host the 2018 World Cup, is attending Sunday's final in Rio de Janeiro to take part in a handover ceremony with Brazilian President Dilma Rousseff and FIFA President Sepp Blatter.

Brazilian officials said Saturday that both Putin and his Ukrainian counterpart, Petro Poroshenko, would be attending the match, but Poroshenko announced Sunday that he wouldn't be going. Talks between Russia and Ukraine over a cease-fire between the rebels and Kyiv's troops have stalled in recent weeks, as Ukrainian troops have succeeded in pushing insurgents out of key towns in the east.