KPN has reiterated its view that shareholders should reject an unsolicited  offer by América Móvil because it substantially undervalues the company.

Mexico-based AM wants to up its stake in the Dutch operator to nearly 28 percent and announced on Friday that it has already crossed the 20 percent barrier.

In a statement, KPN promised to “maintain an active dialogue” with all shareholders, including América Móvil, “for the benefit of the company and its stakeholders”.

But it emphasised that "the current and potential future value of KPN is not reflected in the unsolicited partial offer".

“KPN reiterates its recommendation that shareholders take no action,” it added.

However, it did reveal that its Belgian mobile subsidiary BASE was now officially up for sale.

KPN first mooted the company was up for grabs in April but revealed that the formal sale process will begin in July.

BASE is Belgium’s third largest mobile operator with a market share of around 23 percent.

KPN said the proceeds will be used to improve its “credit profile and financial flexibility”.

The operator said yesterday that the sale of its German mobile unit E-Plus was on hold.