GlaxoSmithKline Plc (NYSE: GSK), Britain's biggest drugmaker, will mount a $2.6 billion hostile takeover bid for Human Genome Sciences Inc. (NASDAQ: HGSI), the company announced Wednesday.

London-based Glaxo previously offered to acquire Human Genome Sciences, of Rockville, Md., for $13 a share last month. The two companies had long had partnerships for sales of several drugs, including Benlysta, which treats lupus. Human Genome shares fell 26 cents to $14.36 after the bid was announced. They'd traded as high as $28.38 over the past 52 weeks.

Human Genome had said it would review its alternatives, but Glaxo said it will not participate in that. At $13, Glaxo's offer is an 81 percent premium to the price at which it first offered to buy the company on April 17.

Glaxo said its offer takes into account the value of Human Genome's Benlysta, Albiglutide and Drapladib products and would be uniquely positioned to deliver on the promises of those drugs after the takeover. The benefits would be a simplified business model for Glaxo, improved R&D returns and immediate liquidity for HGSI shareholders, the UK bidder said.

Human Genome said it would review the offer. But a statement noted that the price is identical to the original bid last month and tender and does not reflect the value inherent in the company. The statement is a common one issued by companies involved in a hostile takeover.

Glaxo said its offer is full and fair, adding that enough time had passed for Human Genome management to come back with a counter-offer. 

Human Genome hired Goldman, Sachs & Co. (NYSE: GS) and Credit Suisse (NYSE: CS) as financial advisers. Legal advisers are Skadden, Arps, Slate, Meagher & Flom LLP and DLA Piper LLP.

Glaxo's U.S. shares fell 55 cents to $45.47 on Wednesday. Its market value is $112.8 billion, compared with Human Genome's $2.86 billion.