U.S. President Barack Obama on Thursday evening called his South African counterpart Jacob Zuma to express his "heartfelt" condolences over the death of former President Nelson Mandela.

During the phone talks, Obama "conveyed how profoundly Mandela's extraordinary example of moral courage, kindness and humility influenced his own life, as well as those of millions around the world," the White House said in a readout of the conversation.

"President Obama reaffirmed that the strong and historic partnership between the United States and South Africa will continue to draw strength from Mandela's legacy as we work together to promote equality, reconciliation and human dignity, and to build a more just and prosperous world," the White House said.

Mandela, the first black president in South Africa, died of illness on Thursday at his home in Johannesburg at the age of 95.

In a televised statement made earlier at the White House, a saddened Obama mourned Mandela's death, saying "he achieved more than could be expected of any man."

In a proclamation signed later, Obama ordered an immediate lowering of flags for Mandela at the White House, upon all public buildings, at all military posts and foreign missions until sunset of next Monday.

As the first black president in U.S. history, Obama had never met Mandela face-to-face in his life. When he visited South Africa in June, the iconic leader was hospitalized with a recurring lung infection.

But Obama and his family visited a jail cell on Robben Island where Mandela was held for 18 of his 27 years in captivity during South Africa's apartheid era.

Mandela served as president from 1994 to 1999. He was released from hospital in early September after an 85-day stay for a recurring lung infection, a result of his longtime imprisonment.