A series of special events has begun in the US in the lead-up to the inauguration of Barack Obama as the 44th US president on Tuesday.

A welcome concert is being held on the steps of the Lincoln Memorial in Washington, with U2, Beyonce and Bruce Springsteen among those performing.

Earlier Mr Obama placed a wreath at the Tomb of the Unknowns in Virginia to remember fallen American servicemen.

Mr Obama held his hand over his heart at the Arlington National Cemetery.

Sunday's concert, which also features musicians Stevie Wonder, Usher, Mary J Blige and Sheryl Crow, is expected to draw a crowd of up to half a million people.

The artists have been asked to perform songs suited to the occasion, rather than their own hits, including A Change is Gonna Come by Sam Cooke.

Historical passages are also being read by singer Queen Latifah and actors Jamie Foxx and Denzel Washington.

Security operation

An unprecedented security operation is under way in the capital ahead of Mr Obama's swearing-in on Tuesday, with the authorities expecting a turnout of up to two million.

Some 240,000 tickets have been issued for the festivities at the Capitol.