WASHINGTON - President Barack Obama and his family are marking Martin Luther King, Jr. Day with a volunteer service project at a local school.

The Obamas joined other volunteers Monday morning at the Browne Education Campus in the District of Columbia.

After greeting volunteers, the president and his family helped build bookshelves in the school's library.

This is the third year in a row the Obamas have participated in a service project on King's holiday.

Washington is home to the Martin Luther King Jr. memorial, where some braved temperatures around 30 degrees (minus 1 Celsius) to visit the 30-foot (9-meter) statue of King.

Dorothy Drake, 61, and her sister Beulah Ashby, 59, were visiting the memorial from North Carolina. The women both went to segregated schools as children and remembered not being able to eat inside certain restaurants, sitting on the back of the bus, and not being allowed to stay in certain hotels.

Ashby said she was proud that King now stands among the presidents honoured with memorials in the nation's capital.

"I woke up this morning, and it gave me great joy to know that I was coming here," Ashby said. "I know it's a piece of stone, and I know it's one man, but it was just pride. Pride. Happiness. Joy, in just knowing that I could come and just have a piece of that history, the changing in the world."

In Columbia, South Carolina, meanwhile, hundreds of people rallied outside the state capitol to honour King and to protest the state's voter identification law.

The U.S. Justice Department has rejected the law. The Obama administration said it didn't pass muster under the 1965 voting rights act, which outlawed discriminatory practices that prevented blacks from voting. On Monday, marchers carried signs that read: "Voter ID(equals)Poll Tax."

U.S. Attorney General Eric Holder was among those slated to speak.

William Barber, president of the North Carolina NAACP, spoke during a morning prayer service and left little doubt that the law would be the day's focus.

He spoke of the many black pioneers who gave their lives so their children and grandchildren could vote, referring to civil rights icons like Medgar Evers. He also referred to three South Carolina State University students gunned down by police during a civil rights protest in 1968.

Barber said it was a critical time to make sure hard-fought voting rights are not lost.

"We are here to stand up, not to back down," Barber said.

Several other states have enacted laws similar to the one passed in South Carolina, which requires voters to show a photo ID before casting ballots. Texas, Alabama, Kansas, Mississippi, Rhode Island, Tennessee and Wisconsin are among them.

Such laws already were on the books in Georgia and Indiana, and they were approved by President George W. Bush's Justice Department. Indiana's law, passed in 2005, was upheld by the U.S. Supreme Court in 2008.

Critics have likened the laws to the poll taxes and tests used to prevent blacks from voting during the civil rights era. Supporters, many of whom are Republicans, say such laws are needed to prevent fraud.

In Holder's prepared remarks Monday, which were released by his office before he spoke, the nation's top attorney pledged to make the nation's elections system more accessible to U.S. citizens. Holder disagreed with those who say parts of the Voting Rights Act are no longer necessary.

"I wish this were the case. But the reality is that -- in jurisdictions across the country -- both overt and subtle forms of discrimination remain all too common," he said.

"And though nearly five decades have passed since Dr. King shared his vision from the mountaintop -- despite all the progress we've made, the barriers we've broken down, and the divisions we've healed -- as a nation, we have not yet reached the Promised Land."