BANGKOK: Police in the Thai capital used water cannons, tear gas and rubber bullets Saturday night to break up a rally by pro-democracy protesters calling for the release of detained activists, constitutional changes and reform of the nation's monarchy.

The rally held outside Bangkok's Grand Palace was a continuation of student-led protests that began last year and have rattled Thailand's traditional establishment, which is fiercely opposed to change, especially with regard to the monarchy.

The demonstrators, who numbered close to 1,000, managed to break through a barrier made of shipping containers outside the ceremonial palace stacked two high.

Police behind the containers responded first with warnings and then by shooting water cannons and rubber bullets.

Police drove the crowd back and while skirmishes continued, the crowds appeared to have dissipated by 10 p.m (1500 GMT).

During the skirmishes, protesters tossed smoke bombs and giant firecrackers at police, and also splashed a royal portrait with paint, but failed in an attempt to set it on fire, though they did burn tires and trash at several locations.

Police Deputy Spokesman Col. Kissana Phathanacharoen said at least six police officers were injured and around five protesters detained.

The city's Erawan emergency services said 11 people in all had been sent to hospitals.