John Atta Mills, Ghana’s president, has died a few hours after being taken ill,in a statement from the president’s office and officials said.

Mills, 68, died on Tuesday in the capital Accra and will be succeeded by Vice-President John Dramani Mahama under Ghana’s constitution, officials said. He had celebrated his 68th birthday only last Saturday.

“It is with a heavy heart … that we announce the sudden and untimely death of the president of the Republic of Ghana,” a statement sent to the Reuters news agency by the president’s office said.

Mills had won international praise as leader of a stable model democracy in Africa, and Ghana remains the only Sub Saharan country Barack Obama, the US president, has visited as recognition for its democratic credentials.

The unexpected death of the leader of the world’s second-largest producer of cocoa comes months before he was due to stand for re-election in December.

Ghana, also a major African gold producer, started pumping oil in 2010 and posted double-digit growth in 2011.

The president’s office said that Mills died a few hours after being taken ill, but no further details were given.

A presidential aide, who asked not to be named, said the president had complained of pains on Monday evening and died early on Tuesday afternoon when his condition worsened.

Very sad. On behalf of my family, I extend my sincere condolences to the govt and people of Ghana

A very sorry to all de ghanians