UPDATE 2-Elliott Advisors ups Actelion stake to over 6 pct

* Elliott is Actelion's largest shareholder

* Elliott previously had nearly 6 pct of Actelion

* Elliott calling for board shake up at Actelion AGM

* Actelion AGM on May 5 (Adds details on Georgeson analysis)

By Katie Reid

ZURICH, April 26 (Reuters) - Activist hedge fund Elliott Advisors has increased its stake in Swiss biotech group Actelion (ATLN.VX) to more than 6 percent over the past week, a spokesman for Elliott said on Tuesday.

The New York-based fund, which has urged Actelion to consider putting itself up for sale after a series of product setbacks, was previously Actelion's largest shareholder with a stake of nearly 6 percent.

Elliott has proposed six new board members and is calling for Actelion's chairman and chief executive to step down from the board at the group's annual general meeting next week.

The fund's move comes just days before the April 28 deadline for shareholders to register their shares.

The spokesman for Elliott also said an analysis done by Georgeson, Elliott's proxy solicitor, showed Elliott has confirmations from 20 percent of shareholders and the likely support of another 15 percent from subscribers of Institutional Shareholder Services (ISS), which advised shareholders to back three of Elliott's boardroom nominees. [ID:nLDE73H1T7]

Georgeson expects 50 percent to 55 percent of all Actelion shareholders to vote their shares at the AGM.

ISS is a U.S.-based shareholder advisory group.

One source close to Actelion said Actelion had strong support from the overwhelming majority of long-only investors, like shareholder BB Biotech, which owns just under 4 percent of the $7.4 billion company.

The source said long-only investors owned more than 50 percent of Actelion.

A banker close to Actelion also noted that no long-term shareholder had publicly supported Elliott in its bid to take control of Actelion's board.

BB Biotech and Rudolf Maag, which own 4.2 percent of the outstanding shares, have both come out in support of Actelion, while it also has the backing of Germany-based independent proxy voting service IVOX and Swiss investor group Ethos.

Actelion has also won support from proxy firm Glass Lewis. [ID:nLDE73K17H]

Actelion shares closed down 0.1 percent at 50.60 Swiss francs, while the European pharmaceuticals sector .SXDP was 0.3 percent weaker. (Editing by Jane Merriman and Steve Orlofsky)