UPDATE 2-KPN rejects iBasis lawsuit, files counterclaim

* KPN says claim aimed at blocking tender offer

* Countersuit filed in Delaware court

* IBasis shares remain above KPN tender offer price

(Adds detail, shares)

AMSTERDAM, Aug 13 (Reuters) - Dutch telecoms group KPN KPN.AS said on Thursday that a lawsuit filed by iBasis Inc. IBAS.O is baseless and aimed at blocking its tender offer for the outstanding shares in the U.S. telecoms provider.

IBasis said that the $48 million offer for the remaining stake for the rest of the company exploits its “depressed stock price” and was grossly inadequate.

KPN, which already owns 56 percent of iBasis, made its tender offer on July 13.

KPN says its offer of $1.55 per share for iBasis is fair and that iBasis would be in a better competitive position if KPN gained full control of the U.S. international wholesale telephone call carrier.

Shares in iBasis were trading at $2.23, down 0.9 percent on Nasdaq at 1556 GMT. KPN shares closed down 0.3 percent in Amsterdam at 10.64 euros.

KPN said in Thursday’s statement that it filed counterclaims against iBasis in Delaware Chancery Court asking it to invalidate a “poison pill” adopted by iBasis management.

“The “poison pill” is a clear violation of iBasis’ own bylaws and the terms of the agreement pursuant to which KPN originally acquired its interest in iBasis and as such, it is not valid,” KPN said.

KPN took a majority stake in iBasis, a wholesale carrier of international long distance telephone calls, in 2006 to boost its international wholesale business. (Reporting by Reed Stevenson; Editing by David Cowell and Gilbert Kreijger)