WASHINGTON, January 21 (RIA Novosti) - US President Barack Obama was officially sworn into office at a private White House ceremony on Sunday, marking the start of his second four-year term.

The Constitution mandates that the US President takes the oath on January 20, but the date falls on a Sunday this year, which means the public inauguration ceremony and festivities will be held on Monday, January 21.

Obama took the oath, administered by Chief Justice John Roberts, in the Blue Room of the White House. He used a Bible that belonged to First Lady Michelle Obama’s paternal grandparents, the White House reported on its website.

“I Barack Hussein Obama do solemnly swear that I will faithfully execute the office of president of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States,” Obama said.

US Vice President Joe Biden was sworn in for his second term at his official residence earlier on Sunday.