Powerful explosions rocked a Russian air base in Crimea on Tuesday, killing one person and injuring 5 others.
Russia's Defense Ministry said munitions blew up at the Saki base, and it emphasized that the installation had not been shelled.
But Ukrainian social networks were abuzz with speculation that it was hit by Ukrainian-fired long-range missiles.
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There was no immediate comment from Ukrainian authorities.
If the base was, in fact, struck by the Ukrainians, it would mark the first known major attack on a Russian military site on the Crimean Peninsula - annexed by the Kremlin in 2014 - and a significant escalation of the conflict.
One person was killed, according to the regional leader of Crimea, Sergei Aksyonov.
The headquarters of Russia's Black Sea Fleet in the Crimean port of Sevastopol was hit by a small-scale explosion delivered by a makeshift drone last month in an attack blamed on Ukrainian saboteurs.