ACCRA, July 24 (Reuters) - Ghana's President John Atta Mills has died unexpectedly, a presidential statement said, and an aide said his death occurred on Tuesday after he took ill on Monday night.

The death of the president of the world's No. 2 cocoa grower comes months before Mills was due to stand for re-election at the helm of the West African country that posted double-digit growth in 2011 and has been praised for its strong democracy in a turbulent region.

"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 Reuters by the president's office said.

It said that Mills, 68, 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.

Mills, who oversaw the start of oil production in Ghana, returned from medical checks in the United States several weeks ago. (Reporting by Kwassi Kpodo; Writing by David Lewis; Editing by Michael Roddy)

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  • Jakaya Kikwete, John Atta Mills, Meles Zenawi

    African leaders attend the Symposium on Global Agriculture and Food Security at the Chicago Council on Global Affairs, Friday, May 18, 2012, at the Ronald Reagan Building in Washington. From left are Jakaya Kikwete, president of the United Republic of Tanzania, John Atta Mills, president of Ghana, and Meles Zenawi, prime minister of Ethiopia. (AP Photo/J. Scott Applewhite)

  • John Atta Mills

    Ghana President John Atta Mills attends the Symposium on Global Agriculture and Food Security at the Chicago Council on Global Affairs, Friday, May 18, 2012, at the Ronald Reagan Building in Washington. (AP Photo/J. Scott Applewhite)

  • Timothy Geithner, John Evans Atta Mills

    Treasury Secretary Timothy Geithner meets Ghana's President John Evans Atta Mills, Friday, March 9, 2012, at the Blair House in Washington. (AP Photo/Manuel Balce Ceneta)

  • Barack Obama, John Evans Atta Mills

    President Barack Obama listens as President John Evans Atta Mills of Ghana, left, speaks in the Oval Office of the White House in Washington, Thursday, March 8, 2012. (AP Photo/Susan Walsh)

  • Barack Obama, John Evans Atta Mills

    President Barack Obama shakes hands with President John Evans Atta Mills of Ghana in the Oval Office of the White House in Washington, Thursday, March 8, 2012. (AP Photo/Susan Walsh)

  • John Evans Atta Mills, Jennifer Klesaris

    John Evans Atta Mills, the President of Ghana, visits the floor of the New York Stock Exchange, Thursday, Dec. 15, 2011, and talks with specialist Jennifer Klesaris. (AP Photo/Dario Cantatore, NYSE)