"We extended his detention," a senior official in Naypyidaw, Myanmar's new administrative capital, told AFP by telephone.

Another official at the Home Affairs Ministry said Tin Oo's house arrest was extended by one year.

Tin Oo is the deputy leader of Aung San Suu Kyi's National League for Democracy party. The international community, as well as local activists, have repeatedly called for the pair to be released.

Tin Oo was arrested along with the Nobel peace prize winner in May 2003, after a pro-government mob attacked their convoy during a political tour of the country's north.

The government has released more than 100 NLD members who were arrested during the incident, but Aung San Suu Kyi and Tin Oo are both still being held under house arrest in Yangon.

He was initially held in prison in Kalay in remote northwestern Myanmar, but in February 2004 was brought back to his home in Yangon, where he has been held ever since.

The United Nations estimates there are about 1,100 political prisoners in Myanmar, which has been ruled by the military since 1962 and was formerly known as Burma.

The NLD won a landslide victory in 1990 elections but has never been allowed to govern.