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Thrombogenics explores ways to boost main drug product Jetrea

* Thrombogenics says considers "strategic options"

* U.S. sales of eye drug Jetrea disappoint in 2013

* Shares rise to four-month high

BRUSSELS, Feb 24 (Reuters) - Belgian biotech group Thrombogenics said it is reviewing how to improve sales of its main product in the United States, where sales have disappointed, sending its shares up 14 percent to a four-month high.

The group has a marketing agreemeent with Novartis unit Alcon outside the United States but is selling eye drug Jetrea, a treatment for vitreomacular adhesion, an ageing-related condition that can lead to blindness, on its own in the U.S.

U.S. sales have been sluggish so far and below the company's own expectations, with analysts estimating a fall in users in the second half of 2013.

"We are starting the strategic exercise with an open mind," Chief Executive Patrik De Haes said.

Thrombogenics shares hit 21.4 euros and were by far the biggest risers on Belgium's Bel20 bluechip index.

"I think they are looking for external parties to help them in the United States. One of the options is to do what they have done in Europe, where they signed a marketing deal with (Novartis unit) Alcon," said KBC analyst Jan De Kerpel.

Thrombogenics was not immediately available to elaborate on what kind of scenario the board was considering. The company said it had hired Morgan Stanley as an adviser.