Washington – A United States government watchdog on Monday criticized Indonesia's Constitutional Court for upholding a law against blasphemy, fearing it may embolden extremists.

The US Commission on International Religious Freedom, a non-partisan body that advises the government, said that blasphemy laws often can cause rather than prevent sectarian strife.

"The Constitutional Court's decision may give extremists cover to enforce a version of religious conformity not shared by the majority of Indonesians," said the Commission's chair, Leonard Leo.

"Hopefully, the Indonesian government will recognize that overturning the blasphemy decree advances its fight against terrorism and extremism and enhances its reputation for religious tolerance and pluralism," he said.

The 1965 law makes it illegal to "publicize, recommend or organize public support" for any religion other than or different to the orthodox versions of six sanctioned faiths: Islam, Buddhism, Hinduism, Catholicism, Protestantism and Confucianism.

It was used in 2008 to force followers of the Islamic Ahmadiyah sect to go underground and is regularly cited by minority groups as a source of discrimination and intimidation.

The Constitutional Court on Monday rejected a petition against the law that was filed by moderate Muslims, minorities and rights groups.

The United States has been seeking to build a broader relationship with Indonesia, the world's largest Muslim-majority country. President Barack Obama is expected in June to travel to Indonesia, where he spent part of his youth.