Ukraine accused Russia on Dec. 16 of looting two of its oil rigs after Crimea-based oil and gas firm Chornomornaftogaz moved the equipment off the coast of the annexed peninsula into Russian waters.

Russia annexed Crimea from Ukraine last year and the loss of the peninsula's valuable energy assets has been a particular sore point for cash-strapped Kiev given a long-running energy dispute between the two countries.

On Dec. 14 Chornomornaftogaz said it had moved the two rigs, worth 25 billion rubles (US$357 million), into Russian territorial waters due to the "the complicated international situation (and) risk of losing vital assets."

While Ukraine had already lost control of the rigs following Crimea's annexation, it described their recent relocation as "large-scale looting."

"The Ukrainian Foreign Ministry expresses its deep indignation in connection with the actions of Russia that violate international law, once again aimed at violating the sovereign rights of Ukraine," the ministry said in a statement.

The annexation of Crimea plunged Kiev's relations with Moscow into a crisis further inflamed by a war between pro-Russian separatists and Ukrainian troops in eastern Ukraine.

Ukrainian state-run energy firm Naftogaz, which owned 100 percent of Chornomornaftogaz, repeated on Dec. 16 that it would seek compensation from Russia in international courts for its annexed Crimean oil and gas assets, which it said were worth $15.7 billion.

New rows have erupted between Russia and Ukraine over Crimea in recent weeks after saboteurs in Ukraine blew up power lines to the peninsula. Delayed repairs to the pylons on the part of Kiev authorities and the suspension of trade links with Crimea prompted Russia to suspend coal exports to Ukraine. ($1 = 70.0900 rubles)