By Guy Faulconbridge and Lidia Kelly
MOSCOW (Reuters) -Ukraine pounded targets in Russia on Tuesday with dozens of drones and rockets in an attack that inflicted serious damage on a major oil refinery and sought to pierce the land borders of the world's biggest nuclear power with armed proxies.
Russia and Ukraine have both used drones to strike critical infrastructure, military installations and troop concentrations in their more than two-year war, with Kyiv hitting Russian refineries and energy facilities in recent months.
Russia said Ukrainian proxies had sought to cross the Russian border in at least seven attacks that Russian forces had repelled.
The Russian-speaking Ukrainian proxies said they had breached the border, a claim denied by Russia.
In one of the biggest Ukrainian drone attacks on Russia to date, Moscow said it downed 25 Ukrainian drones over regions including Moscow, Leningrad, Belgorod, Kursk, Bryansk, Tula and Oryol. Waves of drone attacks continued through the day, the defence ministry said.
Russian officials reported attacks on energy facilities, including a fire at Lukoil's NORSI refinery and a drone destroyed on the outskirts of the town of Kirishi, home to Russia's second-largest oil refinery.
Gleb Nikitin, governor of the Nizhny Novgorod region, said emergency services were working to put out a blaze at the NORSI refinery.
"A fuel and energy complex facility was attacked by unmanned aerial vehicles," Nikitin said on Telegram.
Industry sources told Reuters on condition of anonymity that the main crude distillation unit (AVT-6) at NORSI was damaged in the attack, which means that at least half of the refinery's production is halted. Lukoil declined to comment.
NORSI refines about 15.8 million tonnes of Russian crude a year, or 5.8% of total refined crude, according to industry sources.
It also refines about 4.9 million tonnes of gasoline, 11% of Russia's total, 6.4% of diesel fuel, 5.6% of fuel oil and 7.4% of the country's aviation fuel, according to industry sources.
HITTING RUSSIAN ENERGY
Striking Russian oil facilities is a problem for President Vladimir Putin as he faces off against the West over Ukraine, with domestic gasoline prices sensitive ahead of a March 15-17 presidential election.
Russia imposed a six-month ban on gasoline exports on March 1.
Along with Iran, Saudi Arabia and the U.S., Russia has vast energy reserves but has, since oil was discovered in the wilds of Western Siberia in the 1960s, often relied on Western technology to exploit and refine its crude.
The Kremlin said the Russian military was doing everything necessary and that what it calls its military operation in Ukraine would continue.
Russia says it has destroyed more than 15,000 Ukrainian-launched drones since the start of the war.
BORDER ATTACK
Russia said its forces prevented incursions from Ukraine in the western Belgorod and Kursk regions and inflicted heavy losses on the attackers, after Ukraine-based armed groups said they had launched cross-border raids.
"Ukrainian terrorist formations, supported by tanks and armoured combat vehicles, attempted to invade the territory of the Russian Federation simultaneously," the Russian defence ministry said.
At least two Ukraine-based armed groups purporting to be made up of Russians opposed to the Kremlin said they had launched an incursion across Russia's western border on Tuesday.
Russia denied that the groups, which Moscow casts as puppets of the Ukrainian military and U.S. Central Intelligence Agency, had penetrated its territory, but said the border had come under attack in several places.
The governor of Belgorod, Vyacheslav Gladkov, said one member of the region's territorial self-defence unit had been killed, although he gave no details on what had happened.
The TASS news agency cited the Federal Security Service (FSB) as saying Russian forces had killed 100 people and destroyed multiple armoured vehicles when fighting off attempted incursions.
Russia's defence ministry said Ukraine had fired eight RM-70 rockets and one Tochka-U missile at the Belgorod region.