Russia`s foreign ministry demanded on Friday that Ukraine halt oil exploration in parts of the Black Sea because of a territorial dispute, Russian news agencies reported, according to Reuters.

The activities of Ukrainian energy companies "are of an illegal nature and must be halted," Itar-Tass news agency quoted the ministry as saying.

Political ties between Moscow and Kyiv are strained because of Russian opposition to Ukraine`s NATO membership bid and disputes over the price at which Russia sells gas to its ex-Soviet neighbour.