* Offer of up to 30.50 euros/share follows earlier rebuffs
* Novo's new CEO seeking to bolster blood products unit
* Approach shows demand for biotech assets by large firms (Adds comments from Novo CFO, further reaction and context)
BRUSSELS, Jan 8 (Reuters) - Denmark's Novo Nordisk , the world's biggest maker of insulin, has made a 2.6 billion euro ($3.1 billion) bid for Belgian biotech group Ablynx as it seeks to diversify and strengthen its business for treating rare blood disorders.
Novo went public with the offer on Monday after Ablynx rebuffed earlier approaches and analysts predicted the Danish group, whose new chief executive is seeking new products to bolster growth, would need to raise its bid to win and might face counterbidders.
The approach comes at a time of renewed interest by large drugmakers in acquiring smaller biotech companies to boost their product portfolios.
U.S.-based Celgene clinched a deal to acquire Impact Biomedicines for up to $7 billion on Sunday, while Japan's Takeda Pharmaceutical agreed last week to buy another Belgian biotech group TiGenix for $630 million.
Novo has offered up to 30.50 euros per share for Ablynx, a 60 per cent premium to its Dec. 6 share price, before its first approach.
Ablynx specializes in the research of novel drugs based on nano-bodies found in the immune systems of llamas and alpacas, for which it partners with several of the world's largest pharmaceutical companies.
The main attraction for Novo is Ablynx's experimental drug caplacizumab for the rare bleeding disorder acquired thrombotic thrombocytopenic purpura, which would complement Novo's line-up of blood products focused on hemophilia.
The $11 billion hemophilia market is facing upheaval and Novo stands to lose sales following approval of a new Roche drug Hemlibra.
Hematology has become an increasingly important for Novo, but is still small in comparison to its key diabetes business.
NEW NOVO CEO ACTS
The Danish company said it would pay 28.00 euros per share in cash for Ablynx and an additional 2.50 euros in a so-called contingent value right (CVR) if certain conditions related to its research portfolio were met.
An acquisition would be the first by Novo Nordisk CEO Lars Fruergaard Jorgensen, who took over a year ago. He has said the firm needs external innovation to broaden its product line-up.
Under previous chief executive Lars Rebien Sorensen, Novo sat out a spate of deal-making across the drugs industry in recent years and instead focused on its market-leading position making insulin and other diabetes treatments.
But in March, the company approached Global Blood Therapeutics, a U.S. biotech company focused on serious blood disorders, to discuss a potential takeover, people familiar with the situation said.
Novo Chief Financial Officer Jesper Brandgaard said the current bid could be revised if Ablynx agreed to engage in talks.
"I think it would be natural to update the bid following a detailed discussion with the board of directors of Ablynx," he told a conference call, adding that it would be premature to speculate on any subsequent raise.
Brandgaard also played down the threat of an interloper, saying: "In terms of counter proposals it is not our understanding that any other bidder is pursuing the target."
ABLYNX SHARES SUSPENDED
Ablynx already rejected an offer by the Danish group on Dec. 14 and Novo Nordisk said the new bid, made on Dec. 22, was some 14 percent higher.
"Novo Nordisk regrets that the board of directors of Ablynx has so far declined to engage in any discussions, despite the proposals which have been put forward," it said in a statement.
The Belgian company had was not immediately available for comment on Monday. Belgium's market regulator on Monday suspended Ablynx's shares until further notice.
Analysts at Jefferies said they had a fair value of Ablynx at 29 euros per share, rising to 36 euros under a long term upside scenario.
"We envisage Novo needing to hike the offer and could see counterbids," the analysts said, adding that they see the latest offer as "a low-ball bid."
Tax breaks and other incentives have created a thriving biotech industry in Belgium, with many companies spun off from university projects now listed on the local stock exchange.
Ablynx's shares have almost doubled in price in the past 12 months, buoyed by successful clinical trial data. They closed at 21.20 euros on Friday.
Its products, which are all still undergoing medical trials, target many different diseases such as rheumatoid arthritis, psoriasis or cancer. ($1 = 0.8322 euros) (Additional reporting by Stine Jacobsen in Copenhagen, Ben Hirschler in London and Abinaya Vijayaraghavan in Bengaluru; Editing by Edmund Blair and Keith Weir)