Some 40,000 people have marched in Columbia, South Carolina, to demand the removal of the Confederate flag from the state house.

The rally coincided with Martin Luther King Day, commemorating the civil rights leader who was shot dead in 1968.

The National Association for the Advancement of Coloured People, which started promoting a tourist boycott of the state at the start of the year over the flag issue, organised the march.

The flag - flown by the slave-owning southern states in the American Civil War - is seen by some as part of the country's heritage but by others as a symbol of oppression.

Rev King's son, Martin Luther King III, opened the day with a prayer breakfast at the University of South Carolina.

"The flag is a terrible symbol that brings a lot of negative energy. And while we believe the flag has an appropriate place, it just does not belong on top of the Capitol because it is not a sign of unification," he said.

More than 6,000 marched a week ago in the South Carolina Heritage 2000 rally to show support for keeping the flag flying on the state house.

Positions

Presidential hopefuls have been taking positions over the flag.

Republican candidate John McCain said the issue was divisive but added: "I believe it is a symbol of heritage."

The two Democratic hopefuls - Vice-President Al Gore and Bill Bradley - both oppose the flying of the flag.

"That flag should come down," Mr Bradley said on Sunday.

On Monday, the two men were holding the last electorate debate before the Iowa caucus on 24 January, with Mr Gore leading Mr Bradley by as much as 20% in statewide polls.

Public holiday

Martin Luther King Day has been a public holiday since 1986 and is marked by community service projects around the country, including neighbourhood clean-ups and local house-building projects.

His daughter called on Americans to follow in her father's footsteps by carrying out their own God-given assignments just as Rev King carried out his.

Speaking at the Ebenezer Baptist Church in Atlanta, Georgia, where her father preached, Rev Bernice King told the congregation: "Today, God is calling upon all of us to look at ourselves and ask the question: 'What is it that I am to do to further the cause of freedom, justice and equality?"'

US Vice-President Al Gore, who attended the service, said that the Clinton administration will seek $1.5m in the fiscal 2001 budget to help protect the place where Rev King was born.

'Heart of grace'

"The greatness of a community is most accurately measured by the compassionate actions of its members," Rev King's widow, Coretta Scott King, said on the eve of the holiday.

All one needs to serve, she said, quoting her husband, is "a heart of grace and a soul generated by love.

"The concept here is that service to others is a way to connect to the divine," said Mrs King.

Community events taking place on Monday include a gun buy-back campaign in New Orleans, and an educational fair to teach youngsters about Rev King's life and legacy in Boston.

In Washington DC, volunteers plan to renovate the Martin Luther King Homeless Shelter.

The largest citywide service project is planned in Philadelphia, where more than 18,000 volunteers are expected to join in projects including planting trees, painting schools, clearing out abandoned houses and sorting groceries at food banks.

In New Hampshire, people celebrated Martin Luther King Day for the first time.

In the past, the state had marked a more general Civil Rights holiday.

Utah is considering renaming the state's Human Rights Day in Rev King's honour.

But observance is still far from universal.

While every state gives its workers either a paid or "floating" holiday they can use on Martin Luther King Day, several Southern states combine their observance with honours for Confederate generals Robert E Lee or Stonewall Jackson.