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BRUSSELS, Dec 17 (Reuters) - Belgium's Galapagos has signed a deal potentially worth more than $2 billion with U.S. firm Gilead to develop a drug targeting inflammatory diseases, reviving a project abandoned by former partner AbbVie.

Galapagos will receive a $725 million upfront payment for the development of experimental drug filgotinib, made up of a $300 million licence payment and a $425 million equity investment, the Belgian company said.

Under the deal, Gilead will buy a 15 percent stake of Galapagos at 58 euros per share, a 20 percent premium to the average closing price over the past 30 days.

On top of the upfront payment, Galapagos may receive up to $1.35 billion from Gilead if targets are met, as well as royalties once the drug enters the market.

"In the hands of Gilead, filgotinib has found a strong partner," said KBC analyst Jan De Kerpel. "The deal should also remove doubts investors had on the reason why AbbVie didn't lift the option."

Galapagos shares rose as much as 15 percent to a record 60.55 euros early on Thursday.

In September, AbbVie scrapped a development deal with Galapagos for filgotinib, a new class of medicine that blocks an inflammation-causing enzyme known as JAK1, in favour of its own project instead.

Founded in 1999, Galapagos has several experimental drugs in clinical trials. Filgotinib is its most advanced candidate for the treatment of rheumatoid arthritis and inflammatory bowel disease. Filgotinib may start final clinical trials (Phase III) in 2016 pending regulatory approvals, Galapagos said.

Belgium has become an important hub for biotech firms, partly because of its lenient tax treatment for international research staff and patents.

Galapagos has other research alliances, with Morphosys and Servier, as well as a development partnership for cystic fibrosis with AbbVie.

(Reporting by Robert-Jan Bartunek; editing by Biju Dwarakanath and David Clarke)