Barack Obama has been sworn in as President of the United States for a second term.

The small private ceremony in the White House, took place today, because by tradition, the public celebrations do not take place on a Sunday.

President Obama was joined by his family for the ceremony.

There was no repeat of the mix-up of last time Mr Obama was sworn in, when the Chief Justice John Roberts, mixed up his lines.

Earlier Vice President Joe Biden was sworn in and the two went to Arlington Cemetery to lay a wreath at the tomb of the unknowns.

At least half a million people are expected to attend a public celebration of the inauguration on the National Mall.

A public swearing-in ceremony will be followed by Mr Obama's inaugural address and the inaugural parade down Pennsylvania Avenue, from the Capitol to the White House.

The US Constitution requires the president and vice president to be sworn in on 20 January.