US President Barack Obama Wednesday urged people to honor former South African president Nelson Mandela "through individual and collective acts of service," in a statement marking the anti-apartheid hero's 95th birthday.

Mandela, whose birthday is Thursday, is in the hospital, but admirers around the world were to honor his legacy through a tidal wave of charitable acts for the fifth annual Nelson Mandela International Day.

"Through our own lives, by heeding his example, we can honor the man who showed his own people -- and the world -- the path to justice, equality, and freedom," Obama said.

The US President -- the country's first African-American leader -- went to South Africa two weeks ago, where he had hoped to meet Mandela for the first time since he took office.

Although the meeting was cancelled due to Mandela's poor health, Obama and his family visited the Robben Island jail cell where Mandela spent 27 years as a political prisoner.

Saying they were "deeply moved" by the visit, Obama added "we will forever draw strength and inspiration from his extraordinary example of moral courage, kindness, and humility."

In the prison visitor's book, Obama wrote he was "deeply humbled to stand where men of such courage faced down injustice and refused to yield," he wrote.

"The world is grateful for the heroes of Robben Island, who remind us that no shackles or cells can match the strength of the human spirit."