Botswana's former head of state Festus Mogae has died at the age of 86, President Duma Boko has announced.

"Today Botswana mourns a distinguished statesman and patriot whose life was devoted to the service of his country," Boko announced, adding that Mogae died early on Friday.

The former president, who led Botswana from 1998 to 2008, had been in ill health for some time.

In a statement last month, the government said he was receiving medical care at a hospital in the capital, Gaborone, without disclosing the nature of his illness.

Mogae, the country's thrid president, is widely credited with strengthening Botswana's economic management and governance systems during a period of rapid growth driven by diamond revenues.

In his address to the nation on Friday, Boko hailed Mogae as a leader who "stood firmly for discipline, good governance, economic prudence and the advancement of our nation".

"Under his leadership, Botswana earned its international respect for principled governance," added Boko.

Boko declared three days of national mourning, during which flags will fly at half-mast in honour of the late leader.

Before assuming the presidency, Mogae held senior positions in government including finance minister and later vice-president.

He is also widely credited with steering Botswana's response to the HIV/Aids epidemic. At the time, his country had one of the world's worst infection rates, but an ambitious antiretroviral treatment programme significantly reduced infection and mortality rates.

Even after leaving office, he remained an advocate for HIV/Aids treatment in the region, pushing for free antiretroviral therapy and measures to prevent mother-to-child transmission.

He was subsequently involved in various international advisory and peace mediation roles across the continent.

In 2008, Mogae won the the Ibrahim Prize for Achievement in African Leadership - one of the most prestigious honours for African governance - recognising his democratic leadership and peaceful transfer of power.

As well as the $5m (£3.6m) prize, Mr Mogae was awarded $200,000 a year for the rest of his life.

Mogae was succeeded as president by Ian Khama.

Botswana is one of Africa's most politically stable countries - it has never had a coup and has had regular multi-party elections since independence in 1966.