U.S.-based iBasis Inc. (IBAS) said Thursday it will urge its minority shareholders to vote against a raised takeover offer from Dutch telecom company Royal KPN NV (KPN.AE), but has not closed the door completely.

In a statement, iBasis said that a special committee of its board of directors has decided that KPN's revised offer "significantly undervalues iBasis' current results and long-term prospects." It added that the revised offer was clearly timed to take advantage of its depressed stock price.

However, in the same statement, iBasis said it is willing to recommend "a transaction at a price substantially above KPN's initial offer."

The Massachusetts-based firm, which provides wholesale Voice over Internet Protocol services, said it will uphold its shareholder rights plan, or poison pill, under which it wants to block a takeover by KPN.

The statement comes after KPN last week raised its offer for iBasis ahead of a court hearing at the end of this month in which the Dutch firm is seeking to remove the poison pill strategy.

KPN upped its offer to $2.25 per share from $1.55 a share previously, while the other terms and conditions remained unchanged.

KPN already has a 56% stake in iBasis. The minority stake of approximately 44% not owned by KPN would be valued at $70 million at the $2.25 per share offer price.

KPN declined to comment on the matter.

-By Maarten van Tartwijk; Dow Jones Newswires; +31-20-5715-200