A prominent Israeli human rights group on Wednesday criticized an Israel Defense Forces probe that decided not to press charges in an errant artillery attack that killed 21 Palestinian civilians in the Gaza Strip in November 2006.

The Military Advocate General announced late Tuesday that it was closing the case after its investigation determined the deaths were the result of a "rare and severe" technical malfunction.

In a statement, the human rights group B'Tselem questioned whether the inquiry met proper legal standards: an investigation which is independent, effective, open to review and timely.

The group also called on the IDF to take measures that would prevent similar incidents in the future, and urged it to compensate relatives of the dead.

The shelling was part of a large-scale IDF ground operation in northern Gaza against Palestinian rocket squads, and the civilian deaths provoked the wrath of international groups and human rights organizations. Since then, Israel has rarely used artillery against Gaza.

Fawzi Barhoum, spokesman for the ruling Hamas militant group in Gaza, said the results of the Israeli probe were not surprising.

"This decision is not strange, because every day and every minute dozens of innocent Palestinians are subject to this, either by shelling or by siege or by bullets," he said.

Palestinian militants have continued to launch rockets from Gaza at southern Israeli towns, with at least 30 Qassam rockets slamming in the western Negev Wednesday killing one person, fueling calls for another large military ground operation. Prime Minister Ehud Olmert has ruled that out for now, pointing to the likelihood of high casualties on both sides.