Biotech drugmaker Human Genome Sciences, Inc., said Thursday morning that it received an unsolicited takeover proposal from GlaxoSmithKline for $13 per share, which amounts to nearly $2.6 billion.

Human Genome Sciences is based in Rockville, Md., and has been a partner with GSK in development of the lupus drug Benlysta.

The offer was an 81 percent premium to HGS's Wednesday closing price of $7.17 per share.

HGS did not completely dismiss the offer. The company's statement said its board would explore its options and invited GSK to participate in discussions. HGS asked for more information on other GSK products to see how the two companies mesh.

GSK is based in London, but has facilities in Philadelphia and its suburbs.