KATHMANDU, Sept 7 (Reuters) - Police fired water cannon and teargas and used rattan sticks to break up pro-democracy rallies on Wednesday against Nepal's King Gyanendra, who sacked the government and took total power in February.

Protesters shouting "We don't want autocracy. Democracy can't be destroyed!" threw rocks and bricks at riot police battling to prevent activists from seven main political parties entering the city centre, where anti-king rallies are banned.

Police said 50 protesters had been detained and eight people, including a policeman, hurt. At the same time, authorities said, hundreds of other protesters detained in anti-Gyanendra rallies since the weekend had been freed.

The king says he took power because the government had failed to quell a Maoist revolt that has killed more than 12,500.

The latest protests came as Maoist leader Prachanda, in an interview with pro-rebel weekly Janadesh, said his group was open to talks with the government if it matched their weekend truce and let Nepalis decide their future.

"We are never against talks aimed at giving power to the people," the elusive rebel leader said.

Prachanda, who announced a three-month ceasefire on Saturday to win support from parties opposed to Gyanendra, said an early meeting was unlikely.

The rebels broke ceasefires in 2001 and 2003 after talks foundered on their demand for polls for an assembly to draft a new constitution to decide the future of the world's only Hindu monarchy.

They are fighting to install a single-party communist republic.

The political parties say they are prepared to plan joint protests with the Maoists, but no dates have been decided.