US President George W Bush has written to the founder of China Aid Association, the Rev Bob Fu, commending him for his efforts to bring greater religious freedom to Christians in China.

China Aid Association, based in the US, is a leading group in the campaign against the persecution of Christians in communist China, where Christians are only allowed to worship at official state-approved churches.

"I'm grateful for the good work you are doing to help those affected by religious persecution, and I am deeply moved by your extraordinary acts of service," said President Bush.

"Your faith, courage and dedicated leadership are an inspiration to all, and your devotion to others reflects the love of the Almighty."

Despite attempts by the Chinese government to clamp down on unofficial house churches - who argue that God and not the government should be the head of the church - the unofficial house churches continue to flourish.

Some progress towards full religious freedom in China has been reported by Christians there, including an increase in the availability of Bibles and religious texts in most parts of China, and greater freedom to participate in officially sanctioned religious activities.

Despite these improvements, however, China was re-designated as a "country of particular concern" (CPC) for severe violations of religious freedom last November by US Secretary of State Condoleezza Rice.

Last month, 34 Chinese house church leaders and three Christian leaders from South Korea were arrested during a raid on a house church Bible study in Nanyang city, Henan province.

House church leaders and members face the daily threat of arrest and imprisonment. In 2006, two house church pastors, Liu Yuhua and Wang Zaiqing, were detained and sentenced for printing and giving away Bibles without government authorisation.

Zhang Rongliang, a leader of the China for Christ house church network in Henan province, meanwhile, was sentenced to prison for seven years and six months under the charge of "illegally crossing the national border and fraudulently obtaining a passport" in June 2006.

The People's Republic of China has been designated a CPC every year since 1999.