Ingosstrakh, a Russian insurer, said Friday that it might challenge UK sanctions and seek clarifications about the measures announced by the British government on Thursday against the country's largest insurer.

The UK's sanctions enforcement body OFSI has added Ingosstrakh to its list of Russian entities. Ingosstrakh provides services including ship insurance to Russian oil exporters.

The company told Reuters by email that it was unclear why the OFSI sanctioned Ingosstrakh, since the company operates in strict accordance with all applicable laws and adheres to all compliance procedures.

We will seek clarification and consider legal action if necessary.

The UK imposed separate sanctions Thursday on four vessels of Russia's shadow fleet in an effort to "increase economic pressure" against Moscow.

Reuters cites estimates by a member of the Group of Seven (G7) that sanctions have cost Russia at least $100 billion dollars in lost oil revenue, on top of confiscating $280 billion worth of central bank assets.

Reuters reported that Russian oil exporters charge more for their oil on India's major market than they have ever done since the start of the Ukraine war. This is because a growing number shippers and middlemen are involved in the trade. The impact of Western sanctions against Moscow is weakened as a result.

The designation of Ingosstrakh will not deter operators who are already transporting Russian oil. Those using Ingosstrakh as a liability insurer have decided to work without an insurance company within G7 jurisdiction, according to Malin Hogberg.

The potential impact is based on whether, e.g. Indian authorities may reconsider their position on accepting vessels insured with a newly sanctioned insurer in their ports, said Hogberg. He is also the chair of the sanctions panel of the International Group of top ship insurance companies.

The shadow fleet is estimated at 850 oil tanks, transporting oil to countries like Iran, Venezuela and Russia. Russia has many restrictions on oil exports. (Reporting and editing by Jan Harvey; Jonathan Saul and Vladimir Soldatkin)