Kofi Annan, the former UN secretary-general, has died aged 80.

The Ghanaian national was the first black African to be appointed as the world’s top diplomat and was awarded the Nobel Peace Prize for his humanitarian work during his eight years in the role.

He died in hospital in Bern, Switzerland, in the early hours of Saturday morning.

His death was announced by his family and the Kofi Annan Foundation, which said he had “passed away peacefully” following a short illness.

Mr Annan’s second wife Nane and children Ama, Kojo and Nina were by his side during his last days, they added.

In a statement, the foundation said: “Kofi Annan was a global statesman and a deeply committed internationalist who fought throughout his life for a fairer and more peaceful world.

Mr Annan devoted virtually his entire career to the UN, where he served two terms as secretary-general between January 1997 and December 2006.

His tenure was capped by winning the Nobel Peace Prize, awarded jointly to Mr Annan and the UN in 2001 for “their work for a better organised and more peaceful world”.

“In many ways, Kofi Annan was the United Nations. He rose through the ranks to lead the organisation into the new millennium with matchless dignity and determination,” said current UN secretary-general Antonio Guterres, who described his predecessor as “a guiding force for good”.

“It is with profound sadness that I learned of his passing,” Mr Guterres added.

Tributes poured in from world leaders after news of Mr Annan’s death emerged.

Former British prime minister Tony Blair, with whom the UN chief clashed over the Iraq war, said Mr Annan was “a great diplomat, a true statesman and a wonderful colleague.

Theresa May lauded “a great leader and reformer of the UN” who “made a huge contribution to making the world he has left a better place than the one he was born into”.

Mr Annan faced one of the most turbulent periods in the UN’s history during his time as secretary-general. He took on the post six years after the collapse of the Soviet Union and presided over an era marked by the 9/11 attacks and dominated by the subsequent “war on terror”.

His relationship with the US tested him as a diplomatic leader amid deep global divisions over the Iraq war.

In 2013, he told Time magazine the UN’s inability to stop the Iraq war was his “darkest moment”.

“I worked very hard – I was working the phone, talking to leaders around the world,” he recalled. ”The US did not have the support in the Security Council. So they decided to go without the council. But I think the council was right in not sanctioning the war. Could you imagine if the UN had endorsed the war in Iraq, what our reputation would be like?

“At that point, President [George W] Bush said the UN was headed toward irrelevance, because we had not supported the war. But now we know better.”

Responding to Mr Annan’s death on Saturday, Mr Bush said: “Kofi was a gentle man and a tireless leader of the United Nations. His voice of experience will be missed around the world.”

Much of Mr Annan’s second term was spent at odds with the US, the UN’s biggest contributor, as he leaned on the nation to pay almost $2bn (£1.56bn) in arrears.

He was not immune to criticism; as head of UN peacekeeping operations, Mr Annan came under fire for the world body’s failure to halt the Rwandan genocide in the 1990s.

Challenges from the outset forced him to spend much of his time as secretary-general struggling to restore the UN’s tarnished reputation.

His enduring moral prestige remained largely undented, however, and his cool-tempered elegance and political savvy helped guide him an unprecedented uncontested second term as secretary-general.

When he departed the UN, he left behind a global organisation more aggressively engaged in peacekeeping and fighting poverty, setting the framework for the organisation’s 21st century response to mass atrocities and its emphasis on human rights and development.

“The UN can be improved, it is not perfect, but if it didn’t exist you would have to create it,” he told the BBC world news programme Hard Talk during an interview for his 80th birthday last April.

“I am a stubborn optimist, I was born an optimist and will remain an optimist,” Mr Annan said.

Even after his tenure ended, Mr Annan never completely left the UN orbit. He returned in special roles, including as the UN-Arab League’s special envoy to Syria in 2012.

He remained a powerful advocate for global causes through his eponymous foundation.

UN high commissioner for human rights Zeid Ra’ad al-Hussein, paid tribute to Annan as “humanity’s best example, the epitome, of human decency and grace”.

Mr Zeid, who has criticised major powers during his four-year term, said that whenever he felt “isolated and alone politically” he would go for long walks with Mr Annan in Geneva.

He added: “When I told him once how everyone was grumbling about me, he looked at me – like a father would look at a son – and said sternly: ‘You’re doing the right thing, let them grumble.’”

Former UK prime minister Gordon Brown, who is currently the UN special envoy for global education, said Mr Annan was “a leader of leaders, a wonderful humanitarian and the most compassionate and caring of individuals”.

“Personally modest and always softly spoken, he was a titan amongst world statesman who saw wrong and righted it and who witnessed evil and always fought it,” he added.

“Even in his later years he fought against poverty, injustice and war with all the vigour of youth and I had the privilege of working with him in recent times.”

Former US president Barack Obama said Mr Annan “embodied the mission of the United Nations like few others”.

“His integrity, persistence, optimism, and sense of our common humanity always informed his outreach to the community of nations,” he added. ”Long after he had broken barriers, Kofi never stopped his pursuit of a better world, and made time to motivate and inspire the next generation of leaders.”

The Elders, an elite group of former leaders founded by Nelson Mandela and chaired by Mr Annan, said they were “shocked and deeply saddened” by his death.

In a statement, they described him as “a voice of great authority and wisdom in public and private”.

“His quiet advice on how best to defuse impending crises was in constant demand from all corners of the globe, in particular from Africa,” said deputy chair Gro Harlem Brundtland, the former Norwegian prime minister.

Vladimir Putin paid tribute to a “remarkable person and great politician”.

“I sincerely admired his wisdom and courage, his ability to make balanced decisions even in the most difficult, critical situations,” the Russian president added.

Ghanaian president Nana Akufo-Addo said Mr Annan “brought considerable renown to our country by this position and through his conduct and comportment in the global arena”.