Nelson Mandela, the former president of South Africa, spent the night in hospital battling a lung infection this weekend.
On Saturday, South Africa officials said Mandela was in "serious but stable condition" with his family by his side.
As of this morning, officials had not released any updates on Mandela's condition.
The 94-year-old Nobel Peace prize winner's "condition deteriorated and he was transferred to a Pretoria hospital," early this morning, according to statement from the office of South African President Jacob Zuma on Saturday.
"The former President is receiving expert medical care and doctors are doing everything possible to make him better and comfortable," the statement said. "President Jacob Zuma, on behalf of government and the nation, wishes Madiba [Mandela's clan nickname] a speedy recovery and requests the media and the public to respect the privacy of Madiba and his family."
In April, Mandela spent 18 days in the hospital due to a lung infection and was treated for gall stones in December 2012.
Families throughout South Africa prayed for Mandela's recovery as they attended church services today.
Priest Sebastian Rousso greeted the faithful at the Regina Mundi church in Soweto, which served as a significant landmark during the anti-apartheid movement. Rousso described Mandela as a symbol of reconciliation and played a key role "not only for ourselves as South Africans, but for the world," The Associated Press reported.
Mandela served as the first black president of South Africa from 1994 to 1999.
In 1993, he received a Nobel Peace Prize for his work in ending apartheid through non-violent means.
ABC News' Gillian Mohney and The Associated Press contributed to this report.