The United States warned the world was sliding backwards onreligious freedoms, slamming China for cracking down on Tibetan Buddhists and hitting out at Pakistan and Afghanistan.

As the State Department unveiled its first report on religious freedoms since the start of the Arab Spring, Secretary of State Hillary Clinton said it was a "signal to the worst offenders" that the world was watching.

"New technologies have given repressive governments additional tools for cracking down on religious expression," Clinton told a US think-tank, adding that pressure was rising on some faith groups around the globe.

"More than a billion people live under governments that systematically suppress religious freedom," she stressed.

"When it comes to this human right -- this key feature of stable, secure, peaceful societies -- the world is sliding backward."

The 2011 International Religious Freedom Report noted that last year governments increasingly used blasphemy laws to "restrict religious liberty, constrain the rights of religious minorities and limit freedom of expression."

In China "there was a marked deterioration during 2011 in the government's respect for and protection of religious freedom in China," the report said.

This included "increased restrictions on religious practice, especially in Tibetan Buddhist monasteries and nunneries."