Chinese President Xi Jinping says that China must be on guard against nefarious religious influences from abroad.

His comments over the weekend follow a tightening of religious space that has seen bans on the wearing of veils and beards in the predominantly Muslim region of Xinjiang and the removal of church crosses in eastern China.

"We must resolutely guard against overseas infiltrations via religious means and prevent ideological infringement by extremists," Xi said at a Beijing conference on religions attended by top leaders, according to the official Xinhua News Agency.

He said that religious groups must submit to the leadership of the ruling, and officially atheist, Communist Party, and stressed: "In no way should religions interfere with government administration, judiciary and education."

Authorities in eastern Zhejiang province have over the past two years torn down church crosses and other outward symbols of the Christian faith, saying they violated building codes. Critics say that's a sign of how the rapid growth of Christian groups, at the same time as contacts between Chinese churches and overseas supporters have grown, has made the Communist Party nervous.

China's leaders are also concerned about violence in the far western region of Xinjiang, and say many Uighurs are crossing borders to fight with the Islamic State group in Iraq and Syria with the intention of returning to carry out attacks in China.

Activists representing the Muslim Uighur group say much of the violence is fueled by economic disenfranchisement and restrictions on Uighurs' religious and cultural practices.