Sat Oct 6, 6:18 AM ET

LONDON - Prime Minister Gordon Brown sent a message of support to the people of Myanmar Saturday, as activists took to the streets around the world in a show of solidarity with democracy protesters.

"Today is above all about repeating a firm message: the world has not forgotten -- and will not forget -- the people of Burma," he said.

"We have not forgotten their courage and dignity, taking to the streets in the face of a brutal regime. We have not forgotten the guns and batons, the arrests and murders, which met them."

In London, Buddhist monks will lead a march from the Tate Britain art gallery on the banks of the River Thames to a rally in Trafalgar Square, central London.

On the way, they will tie red headbands similar to those worn by protesters in Myanmar to the gates of the prime minister's official residence in Downing Street.

Brown repeated his assertion that many more protesters have been killed in Myanmar than the military regime admits and described attacks on monks in their monasteries as "appalling".

London also has "very grave concerns" about "hundreds, possibly thousands" of monks, nuns and others who have not been seen since a bloody crackdown on dissent began, he said, urging foreign governments to keep up the pressure.

"The demonstrators who have made sacrifices, and the brave citizens and journalists who have risked so much to get images and information to the outside world, deserve no less," he added.

Brown wants tougher European Union sanctions against Myanmar and has thrown his weight behind UN Secretary General Ban Ki-moon and his special envoy Ibrahim Gambari in efforts towards political reconciliation and democracy.

He also believes the leader of the National League for Democracy, Aung San Suu Kyi, who is under house arrest in the country's biggest city Yangon, should play a central role.

"I salute and share the commitment of those who will send such a powerful message of support to the people of Burma today -- and of condemnation to the regime that seeks to stifle those same Burmese voices," he added.