KYIV, Ukraine (AP) — Powerful explosions rocked a Russian air base in Crimea and sent towering clouds of smoke over the landscape Tuesday in what may mark an escalation of the war in Ukraine.

Ukraine’s Defense Ministry said sarcastically on Facebook: “The Ministry of Defense of Ukraine cannot establish the cause of the fire, but once again recalls the rules of fire safety and the prohibition of smoking in unspecified places.”.

“This Russian war against Ukraine and against all of free Europe began with Crimea and must end with Crimea — its liberation,” President Volodymyr Zelenskyy said Tuesday in his nightly video address.

Earlier Tuesday, Ukrainian officials reported at least three Ukrainian civilians were killed and 23 wounded by Russian shelling in 24 hours, including an attack not far from the Russian-occupied Zaporizhzhia nuclear power plant.

A Russian-installed official in the partially occupied Zaporizhzhia region said an air defense system at the plant would be reinforced in the aftermath of last week’s shelling.

The official, speaking on the condition of anonymity to discuss sensitive information, said “during the last several weeks, Russian officials conducted training in Iran as part of the agreement for UAV transfers from Iran to Russia.”.

officials said later that month that they had seen no evidence yet of Iran supplying Russia with the drones

Ukrainian officials this month said Iran has transferred drones to Russia and some have been used in combat