U.S. network equipment maker Cisco Systems Inc said on Monday it was extending the offer period for its $3 billion bid for Norwegian video conferencing company Tandberg by nine days to November 18.

The terms and conditions set out in the offer document remain in place during the extended offer period, Cisco said in a statement. The one-month tender offer was due to expire on Monday at 1630 GMT.

Chief executive John Chambers said last week he believed the Tandberg deal would be closed but threatened to drop the offer after investors holding about 30 percent of Tandberg shares demanded a higher price than the 153.50 crowns per share offered by Cisco.

Tandberg's board of directors have recommended the offer be accepted. Its shares closed up 0.5 percent at 151.80 crowns.

Cisco made its offer for Tandberg -- its first attempt at a public European takeover -- conditional on 90 percent acceptance.

It was not immediately clear how many shares were tendered before Cisco extended the deadline. A spokesman for Cisco's Norwegian agent Carnegie told Reuters information about this would be released on Tuesday.

Analysts have said Cisco's offer, regardless of when and how it closed, could trigger more deals involving video conferencing firms like No. 2 player Polycom Inc.

Other technology companies like Hewlett-Packard Co also offer high-end video conferencing.

Many analysts had expected Cisco to raise its bid, as acquiring the market leader in video conferencing would accelerate its push in selling video equipment and software.

(Reporting by Richard Solem and Joergen Frich; Editing by Dan Lalor)

($1 = 5.525 crowns)