Finland's former president and Nobel Peace Prize laureate Martti Ahtisaari has died in Helsinki at the age of 86 after battling Alzheimer's disease, the president's office said Monday.

"It is with deep sadness that we have received the news of the death of President Martti Ahtisaari," the current president, Sauli Niinisto, said in a statement.

Serving as president from 1994 to 2000, the mediator negotiated an end to conflicts around the globe, from Indonesia to Kosovo and Namibia, earning him worldwide recognition and a Nobel Peace Prize in 2008, as part of  a formidable career spanning over 40 years.

The former UN diplomat was credited with overseeing the 2005 reconciliation of the Indonesian government and Free Aceh Movement rebels, bringing an end to a three-decade conflict that killed some 15,000 people.

The two sides described Ahtisaari as steely during the talks, but gifted with a sense of humor and warmth on the sidelines.

"I have enormous amounts of patience. I don't usually get angry, but I can be tough," he later said, adding that he felt the key to his success was an ability to understand people.

Ahtisaari also helped lead Kosovo down the path toward independence, even though his intense efforts failed to clinch an agreement with Serbia before Pristina unilaterally declared independence in 2008.

Ahtisaari withdrew from public life in September 2021 as he struggled with Alzheimer's disease.