File photo taken on Dec. 19, 2006 shows then UN Secretary-General Kofi Annan smiling during his final press conference at the United Nations headquarters in New York. (Xinhua/Zhao Peng)

GENEVA, Aug. 18 (Xinhua) -- UN and European leaders on Saturday paid their tributes to former Secretary General of the United Nations (UN) Kofi Annan, who passed away on the day at the age of 80 in a Swiss hospital.

In a mourning statement issued immediately after Annan's passing, UN Secretary-General Antonio Guterres described Annan as "a guiding force for good", saying that "in many ways, Kofi Annan was the United Nations".

Michael Moller, Director-General of the United Nations Office at Geneva, said that with the passing of Annan, "Humanity has lost its strong moral voice, and I lost my mentor, my role model and great friend".

"He was an exceptional human being, with an amazing balance, infallible political instinct and ever present compassion, always caring for others, particularly the less fortunate of us," he said.

Joining the UN system in 1962 as an administrative and budget officer with the World Health Organization in Geneva, Annan has spent much of his life in this Swiss city, including being as the UN High Commissioner for Refugees and later as the head of the Kofi Annan Foundation.

"Since the 1980s, when he worked in Geneva until his last years he remained an enduring voice on behalf of refugees and all who are oppressed," UN High Commissioner for Refugees Filippo Grandi said.

In him, the millions worldwide forced to flee wars and persecution had a constant champion at the highest international levels, Grandi added.

For UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein, Annan was "irreplaceable" and "humanity's best example and the epitome of human decency and grace".

Audrey Azoulay, Director-General of UNESCO, called Annan as "a great defender of peace", saying that he was the very embodiment of peace and of a resolutely modern vision of the United Nations.

"His conviction that a culture of peace should be developed was fully in line with the mandate and daily commitment of UNESCO," she said.

While mourning Annan, European Commission President Jean-Claude Juncker said that Annan, as an old friend and inspiration for him, had devoted his life to making the world a more peaceful and united place.

"His achievements as UN Secretary-General were rightly recognized with the Nobel Peace Prize and many other accolades throughout his life. But the greatest recognition we can give Kofi Annan is to keep his legacy and his spirit alive," he added.

French President Emmanuel Macron on Saturday also paid tribute to the former UN chief, saying that the world will never forget his calm and resolute approach to matters, nor the strength of his commitments.

"France pays tribute to him," Macron wrote on his twitter account.

A statement released by the office of Italian President Sergio Mattarella said that with Annan's demise, the international community lost a landmark figure, and the United Nations lost a former leader of peace, human rights and sustainable development.

British Prime Minister Theresa May also expressed her sadness at Annan's death. Saying that Annan was a great leader and reformer of the UN, the British prime minister said that Annan had made a huge contribution to making the world he has left a better place than the one he was born into.

Describing Annan as a great peace builder, Finnish President Sauli Niinisto said Saturday that with the passing of the former UN chief, the world has lost "a most staunch supporter of the rule-based international order".

"It was with great regret that I received information about the death of former UN Secretary General Kofi Annan; in our memory he will remain as a person who worked tirelessly to protect human rights and improve living conditions in Africa," Polish President Andrej Duda wrote in a condolence telegram.

Born in Ghana in 1938, Annan was the seventh Secretary-General of the United Nations, served from 1997 to 2006 and was the first to emerge from the ranks of United Nations staff.

As Secretary-General, one of Annan's main priorities was a comprehensive program of reform aimed at revitalizing the United Nations and making the international system more effective.

He was a constant advocate for human rights, the rule of law, the Millennium Development Goals and Africa, and sought to bring the Organization closer to the global public by forging ties with civil society, the private sector and other partners.

Annan was awarded the 2001 Nobel Prize for Peace, jointly with the UN.