Investors holding 24 per cent of the shares in Tandberg look set to block Cisco’s $3bn bid for the Norwegian video conferencing company, raising hopes that the US networking company might sweeten the offer.

Cisco offered NKr153.5 a share for Tandberg this month in a move designed to make it a dominant force in the growing video communications market. The Cisco deal was recommended by the Tandberg board, but a group of mainly small shareholders including the Oslo Pension Fund and Rasmussen Group on Thursday said they would not sell shares to Cisco under the current offer.