The White House Press Secretary Jay Carney, said the US is closely monitoring the situation.
"At this point, I think I can say that we are assessing - that we are monitoring the situation and understand from the reports that former South African President Nelson Mandela is in critical condition," he told reporters at his daily news conference.
"Our thoughts and prayers are with him, his family, and with the people of South Africa. I wouldn't want to speculate about the impact of Mr. Mandela's health on the President's trip," he said.
"The President obviously has long seen Nelson Mandela as one of his personal heroes, and I think he is not alone in that in this country or around the world. And we all express our thoughts and prayers -- or note that our thoughts and prayers are with the Mandela family at this time," Carney said.
Yesterday, South African President Jacob Zuma said Mandela is still in a critical condition, assuring the nation that doctors were doing their best to ensure the "well being and comfort" of the 94-year-old anti-apartheid icon in his third week of hospitalisation.