LOS ANGELES - DECEMBER 15: President Jimmy Carter smiles as he attends an autograph session for his book "Sharing Good Times" at Borders Books and Music December 15, 2004 in Westwood, California. (Photo: Mark Mainz /Getty Images) 
Carter, 98, who has lived longer after leaving the White House than any former president in U.S. history, was a Democrat who served from January 1977 to January 1981.
"He has the full support of his family and his medical team. The Carter family asks for privacy during this time and is grateful for the concern shown by his many admirers," the center said in a statement.
In recent years, the Georgia native suffered from several health issues including melanoma that spread to his liver and brain, although he had responded well to treatment he received.
The former peanut farmer's rocky four years at the helm of the country were marred by economic woes at home and the Iran hostage crisis that ended just after he left office. But Carter also played a central role in brokering the Camp David accords that led to the landmark Egypt-Israeli peace treaty.
He was swept from office in an electoral landslide in 1980 as voters embraced Republican challenger Ronald Reagan, the former actor and California governor.
However, Carter rehabilitated his legacy as he worked energetically for decades on humanitarian causes.
He was awarded the Nobel Peace Prize in 2002 in recognition of his "untiring effort to find peaceful solutions to
international conflicts, to advance democracy and human rights, and to promote economic and social development."
He could also often be seen, hammer in hand, helping to build affordable houses as a volunteer for Habitat for Humanity.
Carter and his wife Rosalynn, whom he married in 1946, have four children. DM