A senior adviser to the European Court of Justice says European Union economic sanctions imposed on Russian companies are valid in the main under the EU's common security and defense policy.

Advocate General Melchior Wathelet issued the opinion Tuesday in response to a challenge the Russian oil and gas producer Rosneft filed before a British court.

Rosneft is seeking annulment of an EU leaders' decision in July 2014 to impose restrictive measures on it and other Russian companies following Russia's annexation of Crimea from Ukraine.

Wathelet found the sanctions valid with the exception of one regulation he said was in contradiction with the EU leaders' original decision. He asked the EU court to formally adopt his non-binding conclusions. The Luxembourg-based tribunal is expected to rule within three to six months.