MOSCOW (Reuters) -Ukraine attacked Russian nuclear-capable long-range bombers at a military base in Siberia on Sunday, the first such attack so far from the front lines more than 4,300 km (2,670 miles) away, according to pro-Russian bloggers. Unverified video and pictures posted on social media showed Russian strategic bombers - whose purpose is to drop nuclear bombs on distance targets - on fire at the Belaya air base north of Irkutsk. Reuters was unable to immediately verify the footage but in Kyiv, a Ukrainian intelligence official told Reuters that Ukraine's domestic security agency, the SBU, conducted a large drone attack on over 40 Russian military aircraft.