VIENNA (Reuters) - President Barack Obama’s decision not to prosecute CIA interrogators who used waterboarding on terrorism suspects amounts to a breach of international law, the U.N. rapporteur on torture said.

“The United States, like all other states that are part of the U.N. convention against torture, is committed to conducting criminal investigations of torture and to bringing all persons against whom there is sound evidence to court,” U.N. special rapporteur Manfred Nowak told the Austrian daily Der Standard.

Nowak did not think Obama would go as far as to seek an amnesty law for affected CIA personnel and therefore U.S. courts could still try torture suspects, he said on Saturday.

Obama has affirmed his unwillingness to prosecute under anti-torture laws CIA personnel who relied in good faith on Bush administration legal opinions issued after the September 11 attacks.

Obama said he had ended harrowing techniques used against detainees by Bush-era CIA personnel, but that U.S. intelligence agents still operated in a dangerous world and had to be confident they could perform their jobs.

Nowak, an Austrian, suggested an investigation by an independent commission before suspects were tried and said it would be important for all victims to receive compensation.

Human rights advocates have attacked Obama’s decision, saying charges were necessary to prevent future abuses and hold people accountable. Some U.S. lawmakers have called for public investigations.

The four memos Obama released approved techniques including waterboarding, week-long sleep deprivation, forced nudity and putting insects in with a tightly confined prisoner.

His administration also said it would try to shield CIA employees from “any international or foreign tribunal” -- an immediate challenge to Spain where a judge has threatened to investigate Bush administration officials.