Burmese authorities detained 12 opposition party members who called for the release of pro-democracy leader Aung San Suu Kyi as she marked her 63rd birthday under house arrest, witnesses said.

The 12 people were taken into an empty truck after dozens of Suu Kyi’s party members gathered outside the party headquarters in Rangoon, the country’s biggest city. The protesters were shouting slogans calling for the government to immediately release Suu Kyi “who has been unfairly detained”.

The country’s ruling junta last month extended the house arrest of the Nobel Peace Prize laureate for the sixth straight year in face of international protest. The crowd dispersed – some running back into Suu Kyi’s National League for Democracy party headquarters – after six empty trucks approached. Some 40 plain-clothes security officials and other pro-junta men were stationed around the headquarters.

Earlier in the day, the party celebrated her birthday by offering meals to Buddhist monks at its party headquarters several miles from her home.

Suu Kyi has spent more than 12 of the last 18 years under detention. Her party swept national elections in 1990 but the military rulers refused to honour the results and instead are pursuing a so-called “road map to democracy” with the junta in full control of the process.

Meanwhile, Prime Minister Gordon Brown and French president Nicolas Sarkozy issued a joint message of support Aung San Suu Kyi to mark her birthday.

In their open letter, Mr Brown and Mr Sarkozy – who meet in Paris today ahead of an EU summit – promised Ms Suu Kyi: “We will not forget you or your people in this struggle. We wish to use this opportunity, on the occasion of your birthday, to reaffirm our commitment to your lifelong struggle to achieve democracy and humanity in Burma.

“You have sacrificed your freedom for the freedom of others. You have shown exceptional courage and dedication to your people. Your release from house arrest and your freedom to participate in Burma’s political future remain essential.”

The Press Association