MOSCOW — The Russian government announced a state of emergency in the disputed Crimean peninsula late Saturday evening after power to the region was suddenly cut in an apparent act of sabotage in neighboring Ukraine.

Two electricity transmission towers were destroyed in at least one explosion Saturday evening in Ukraine's Kherson region, cutting electricity from mainland Ukraine and plunging the entire Crimean peninsula into darkness. The towers had sustained severe damage in an earlier bomb blast Friday, but remained functional until Saturday's attack.

Tensions have soared between Russia and Ukraine since Crimea was annexed in March 2014 after Russian troops wearing uniforms with no identifying markings seized key infrastructure, and pro-Russian leaders held a snap referendum to secede from Ukraine.

"Crimea has been fully shut off," said Viktor Plakida, head of Crimea's state energy company, the Russian state news agency TASS reported. Russian officials said they were using mobile generators to return power to crucial infrastructure, including hospitals.

Pro-Ukrainian activists are staging a "blockade" of Crimea near the site of the transmission towers, and have urged the Ukrainian government to halt deliveries of food to the peninsula. Ukrainian news agencies said the protesters denied that they had attacked the towers.