The groups had been ordered in a 2004 civil case to pay 156 million dollars to the family of 17-year-old David Boim, killed in 1996 in an attack. A federal appeals court ruled Friday that the groups' role was not fully established.

It ordered a new trial to examine more closely the links between the organizations and the boy's death.

"The Boims will have to demonstrate an adequate causal link between the death of David Boim and the actions" of the groups, the court ruling said.

"This will require evidence that the conduct of each defendant, be it direct involvement with or support of Hamas's terrorist activities or indirect support of Hamas or its affiliates, helped bring about the terrorist attack that ended David Boim's life."

The groups had been charged with taking part in terrorism by aiding or financing Hamas, a powerful Islamist movement in the Palestinian territories.

"The Boims' theory ... was that in promoting, raising money for, and otherwise working on behalf of Hamas, these defendants had helped to fund, train, and arm the terrorists who had killed their son," the ruling said.

The defendants included the American Muslim Society and the Holy Land Foundation for Relief and Development, which was the biggest Muslim charity in the United States until it was outlawed after the attacks of September 11, 2001.

The foundation also faces separate criminal charges for alleged links with Hamas. It is charged with giving 36 million dollars to committees controlled by the movement from 1992 to 2001.

A leading US Muslim rights group, the Council on American-Islamic Relations (CAIR), welcomed the appeal court's decision Friday.

"This landmark ruling is a strong rejection of the recent disturbing trend of political lawsuits against American Muslims who have committed no crime other than providing humanitarian aid to Palestinians," it said in a statement.

"CAIR deplores the murder of David Boim and hopes that the actual wrong-doers are brought to justice."