Burmese opposition leader and Nobel Peace Prize winner Aung San Suu Kyi spent her 64th birthday in prison Friday, as demands for her freedom erupted across the internet and at rallies worldwide.

Celebrities Brad Pitt, Julia Roberts, Paul McCartney, Madonna and David Beckham joined Nobel laureates and world leaders in calling on the military junta in Burma, also known as Myanmar, to release Suu Kyi, who has now spent 14 birthdays in detention.

Many posted online messages on social networking sites such as Twitter and Facebook in what human rights groups called an unprecedented and powerful tool to harness support for Suu Kyi.

"Daw Aung San Suu Kyi will celebrate her birthday by treating the people around her [her guards] to rice and chocolate cake," said lawyer Nyan Win, who left gifts for her at the prison Friday including a chocolate cake, an apple cake, bouquets of orchids and 50 lunch boxes of biryani rice.

"Daw" is a term of respect in Myanmar.

Sparrows, doves: symbols of freedom

"She really appreciates the efforts and said she was sorry she wasn't able to thank everyone individually," Nyan Win said.

At a ceremony outside Suu Kyi's National League for Democracy party's headquarters in Rangoon, supporters released 64 sparrows, 10 doves and coloured balloons into the sky.

Suu Kyi has spent more than 13 of the last 19 years in detention, mostly under house arrest. Her party won Myanmar's last elections in 1990 but the junta rejected her victory.

After an uninvited American swam to her tightly guarded lakeside home last month, she was arrested and is now on trial for violating the terms of her house arrest.

"We must not stand by as she is silenced again. Now is the time for the international community to speak with one voice," says part of a 64-word message on a new website signed by dozens of dignitaries and celebrities including George Clooney, Sarah Jessica Parker, Robert De Niro, Nicole Kidman, director Steven Spielberg and fellow Nobel Peace Prize winners Elie Wiesel and Desmond Tutu.

Artist Yoko Ono tweeted: "FREE Daw Aung San Suu Kyi NOW!"

The Associated Press