But the White House refused to speculate whether the president would change his plans to account for Mandela's deteriorating health.

"I think it's really hard to say. And I think it just wouldn't be appropriate to speculate on that. Right now, we're all wishing for his recovery," Carney said.

"You know, the president, obviously, has long seen Nelson Mandela as one of his personal heroes," he added. "And I think he's not alone in that in this country or around the world. And, you know, we all, again, express our thoughts and prayers, our note that our thoughts and prayers are with the Mandela family at this time."

The president is scheduled to leave for Africa on Wednesday, with a visit to South Africa starting Friday. Obama had initially planned to meet with Mandela during the trip, but those plans have been put on hold as the former president's family evaluates his health.

Mandela became the first black president in South Africa in 1994, shortly after being freed from 27 years of imprisonment. He has not made a public appearance since the World Cup in 2010.