Mumbai: State-owned China Petroleum & Chemical Corporation (Sinopec) has approached London-listed oil and gas explorer Imperial Energy Corporation Plc, in a development that could derail a planned takeover of the London-based oil explorer by ONGC Videsh Ltd, the overseas arm of the Oil and Natural Gas Ltd (ONGC) of India.

Sinopec, which made an approach to Imperial last week, is currently in the process of conducting due diligence ahead of making a formal offer.

''The board of Imperial confirms that it has received another approach in relation to a possible cash offer for the company,'' Imperial Energy said in a website statement without identifying the suitor.

OVL, which had offered to acquire Imperial for 12.90-pound a share, or a total of 1.3 billion pound ($2.5 billion), may now have to enter a bidding war with the Chinese firm. (See: ONGC in bid to acquire Russia's Imperial Energy)

Imperial, with a number of oil assets in Russia and other countries of the former Soviet Union, had plans to raise its oil production of about 10,000 barrels of oil a day in December last year to 80,000 barrels a day by the end of 2011.

Imperial Oil, founded by chairman Peter Levine in 2004, has been the subject of several takeover attempts, including one by Russian energy giant Gazprom.

The news was first brought out London's Sunday Telegraph on Friday, when it reported that Imperial had agreed to let Sinopec begin due diligence ahead of a possible bid.

Imperial said it would make further announcements about the offer ''when appropriate."

Imperial Energy, founded in 2004, is an independent oil and gas exploration company with holdings mainly in western Siberia and Kazakhstan.

Shares of Imperial, one of the worst market performers among mid-sized oil companies on the London Stock Exchange, rose as high as 14.27 pounds against its 637 pence low seen last year.

If the Sinopec bid for Imperial is successful, it would be the largest takeover of a London-listed British company by a Chinese corporation.

The Chinese counter offer comes even as OVL has entered the final stages of talks with Imperial.

OVL had lost out on Canadian firm Encana's properties in Ecuador when a Chinese consortium bid $1.42 billion. It also lost PetroKazakhstan to China National Petroleum Corp's $3.6 billion bid. In Angola, it lost out a 50 per cent in BP-operated Block 18 when the African nation preferred China.