Malaysia accused Washington on Friday of meddling in its domestic affairs by commenting on sodomy allegations facing opposition leader Anwar Ibrahim.
Anwar has rejected accusations of sodomy made by a male aide last weekend, saying they were part of a conspiracy to keep him from seizing power from Malaysia's ruling coalition. Government leaders have denied trying to frame Anwar.
US State Department spokesman Tom Casey on Monday urged Malaysia to keep politics and the legal system separate, saying "we will certainly oppose any use of law enforcement or judicial procedures for anything other than legitimate purposes of the law."
Malaysian Foreign Minister Rais Yatim told reporters that he sent a letter to US Secretary of State Condoleezza Rice on Friday expressing regret about those comments, which he said were "" and tantamount to interference in Malaysia's affairs.
Rais said he expected a response from Washington, but did not elaborate.
Anwar, a former deputy prime minister, revived his political career in March when his three-party opposition alliance won 82 seats in the 222-member Parliament, the strongest performance ever for the opposition.
Anwar insists he is close to engineering enough defections from the ruling coalition to bring down Prime Minister Abdullah Ahmad Badawi's administration. He has openly aspired to be the country's next leader if the opposition comes to power.