A U.S.-based human rights watchdog today accused Palestinian leader Yasser Arafat of "political responsibility" for suicide bombings against Israeli civilians and condemned such attacks as crimes against humanity.

The group, Human Rights Watch, said that though its investigation found no evidence to support Israel's charges that Arafat orchestrated such attacks, his Palestinian Authority is at fault for failing to rein in and punish militants behind the bombings.

"Arafat and the Palestinian Authority bear a high degree of political responsibility for the atrocities that occurred," Kenneth Roth, the rights group's executive director, said in a statement marking the release of a report on suicide bombings.

With its charges, Human Rights Watch added its voice to frequent accusations by the Israeli government that Arafat is responsible for the suicide attacks because of his failure to do enough to stop them. The report called on Palestinian officials to make a serious effort to arrest and prosecute those who plan and carry out attacks. It also urged Israel to assist by halting strikes that have crippled the Palestinians' security infrastructure.

The group, which in previous reports has accused Israel's army of rights abuses against Palestinians during the two-year-old uprising, appealed to Israel to abide by international humanitarian norms in its military response to bombings.

But Human Rights Watch reserved its sharpest criticism for Palestinian groups -- including the Islamic Resistance Movement, or Hamas; Islamic Jihad; and the al-Aqsa Martyrs Brigades, an armed offshoot of Arafat's Fatah movement -- for attacks that have killed scores of Israelis.

"The people who carry out suicide bombings are not martyrs; they're war criminals," Roth said. The bombings "clearly fall under the category of crimes against humanity."

Human Rights Watch also called for criminal investigations of such officials as the Hamas spiritual leader, Sheik Ahmed Yassin, who it said "openly espoused, encouraged or endorsed" attacks.

"Human Rights Watch did not find evidence that Arafat or the Palestinian Authority planned, ordered or carried out suicide bombings or other attacks on Israeli civilians or that they were able to exercise effective control over the actions of the perpetrator groups," it added.

A Palestinian Authority spokesman said he would have no comment until he had a chance to read the 170-page document. But Nafez Azzam, a senior Islamic Jihad leader in Gaza, said the report was "flagrantly biased" in favor of Israel.

Human Rights Watch found no proof that Yasser Arafat had ordered attacks against Israeli civilians.