Thousands of US anti-war protestors have demonstrated in the city of Denver where the Democratic national convention is set to begin.

The protestors took to the streets while an estimated 5,000 police and security personnel, including the Secret Service, were on high alert.

The demonstrators protested the war in Iraq and any potential war the US might fight against Iran, calling on the US Democratic presidential candidate Barack Obama to stick to his initial anti-war stance.

Among the protestors was the US peace activist Cindy Sheehan whose son was killed in Iraq war. She criticized Obama for kowtowing to the Republicans and showing flexibility in his Iraq policy.

"Neither Republicans nor Democrats represent the people. They've taken away more of our freedoms. It's now easier to spy on us," she told the crowd.

Approximately 50,000 people including state delegates, superdelegates, the media, party leaders, politicians and volunteers are expected to gather for the Democratic National Convention (DNC) which kicks off Monday at the Pepsi Center in Denver, Colorado.

Senator Obama will claim the nomination of the party to run for the presidency with his running mate and Chairman of the Senate Foreign Affairs Committee, Joe Biden, on the final day, Thursday.

AO/BGH