Barack Obama has become the 44th president of the United States, during an inauguration ceremony witnessed by at least one million people in Washington DC.
Obama was sworn in as the US commander-in-chief just after noon local time (1700 GMT) on Tuesday, becoming the first African-American to hold the post.
Obama acknowledged that the United States faces several challenges, from military campaigns in Iraq and Afghanistan to economic concerns at home.
About 8,000 police officers were deployed and 32,000 military personnel were on duty or standby for the inauguration.
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Barack Obama takes the Oath of Office as the 44th President of the United State