By Simon Kennedy, MarketWatch

LONDON (MarketWatch) -- Shares of oil giant BP PLC declined in a flat market Thursday, pulling back after the U.S. government filed a civil lawsuit against the company over the Gulf of Mexico oil spill.

Other European markets eked out small gains as European Union leaders gathered in Brussels to discuss the sovereign-debt crisis. See Europe Markets.81.1

The FTSE 100 index closed the London session virtually unchanged at 5,881.2.

Shares of BP (BP) ranked as one of the top decliners on the index, down 1.3%.

The U.S. government said Wednesday that it is suing the company and eight other defendants, alleging that negligence and lax safety procedures led to the historic Gulf oil spill earlier this year.

"While not wholly unexpected, the move by the U.S. Justice Department will nevertheless shine the spotlight once again on the risks associated with deepwater drilling in particular, and insurance for any potential liabilities," said Goodbody Stockbrokers analyst Gerry Hennigan.

Separately, the latest round of U.S. embassy cables released by WikiLeaks reportedly highlighted similarities between the Gulf of Mexico disaster and a little-reported major gas leak at BP's operations in Azerbaijan in 2008.

Other London-listed energy stocks advanced, including BG Group PLC , which gained 0.5% after the company said it's drilled an 11th successive well in a concession in the Santos Basin located in waters off the coast of Brazil.

Meanwhile, pharmaceutical stocks added to the previous session's gains, which were driven by Novartis AG's (NVS) deal to acquire the remaining stake in Alcon Inc. (ACL) and restart its share-buyback program.

Hopes of cash returns from other drug companies have lifted the sector, with GlaxoSmithKline PLC (GSK) shares rising 0.2% Thursday.

Also making gains, shares of Serco Group PLC stood out as the strongest performer within the main index, rising 4.1% after the outsourcing company said it remained on track to deliver strong organic revenue growth.

 
 
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