U.S. museums are increasingly dodging the restitution of Nazi-looted artwork by using legal maneuvers to avoid resolving the cases on their merits, according to a report by the World Jewish Restitution Organization (WJRO) released Thursday.

The report said the tactic has grown in recent years.

"American museums have an obligation to ensure that claimants get a fair chance to get a hearing on their case," said Gideon Taylor, chair of WJRO operations. "That increasingly is not happening in U.S. museums."

The defense by museums also likely deters claimants of coming forward because they face an uphill legal battle, according to the report.

The report cites five cases in which the courts sided with the institutions, which won their cases on legal technicalities such as statute of limitations. A sixth cases involving a disputed Camille Pissaro painting donated to the Fred Jones Jr. Museum of Art at the University of Oklahoma in 2000 is pending.

The Oklahoma museum has backed the Jones family saying the donated piece of art was purchased “in good faith from a reputable art dealer, with legitimate and verified title."

"We continue to hope for a resolution that will be fair to all parties," it added.

The report also shows that other countries have taken a different approach to settling claims of stolen Nazi-era art, establishing tribunals or special venues where these issues can be heard based on the merits and not technical grounds.

"We're not saying every claimant is right and that every claim is a valid claim. We're saying let the claim be heard by a neutral body," Taylor said. "If the museums are confident in their interpretation of the facts, then they should be confident to let the court adjudicate whether that's right or not."

Among its recommendations, the report says the American Alliance of Museums should ensure museums comply with its guidelines "by abstaining from blocking claims on technical grounds." Museums that fail to do so should be subject to a review of their accreditation with the AAM, it says. It also recommends legislation to extend statutes of limitations for Holocaust-era restitution claims.

The museum organization said in a statement that it "takes seriously issues surrounding the question of Nazi-era looted art and is committed to ensuring museums act ethically and in accordance with standards."

The Associated Press contributed to this report.