The flag at the UN headquarters in New York is flying at half-mast as the organization marks the death of former Secretary-General Kofi Annan, Aug. 18, 2018. (Xinhua/Li Muzi)

UNITED NATIONS, Aug. 18 (Xinhua) -- The flag at the UN headquarters in New York is flying at half-mast this Saturday as the organization marks the death of former Secretary-General Kofi Annan.

Officials from across the UN system have been paying tribute to the man who led the global body for a decade, starting in January 1997.

He was Secretary-General during what has been described as one of the darkest days in the organization's history: the Aug. 19 2003 bombing of the UN premises in Baghdad, Iraq, the first mass attack targeting the UN that killed 22 members of its staff.

Incumbent UN Secretary-General Antonio Guterres praised Annan as "a guiding force for good," saying "in these turbulent and trying times, his legacy as a global champion for peace will remain a true inspiration for us all."

Guterres recalled being selected by Annan to serve as UN High Commissioner for refugees, saying he felt "deeply honored by his trust" and Annan was "someone I could always turn to for counsel and wisdom."

"He provided people everywhere with a space for dialogue, a place for problem-solving and a path to a better world," he added.

Flowers are put under the portrait of former Secretary-General Kofi Annan at UN headquarters, Aug. 18, 2018. (Xinhua/Li Muzi)former Secretary-General Kofi Annan, Aug. 18, 2018. (Xinhua/Li Muzi)

For Zeid Ra'ad Al Hussein, the outgoing UN High Commissioner for Human Rights, Annan is simply "irreplaceable."

"Kofi was humanity's best example, the epitome, of human decency and grace. In a world now filled with leaders who are anything but that, our loss, the world's loss becomes even more painful," he said in a statement.

Before taking the reins of the organization, Annan held various senior level positions at the headquarters and in the field. At one point he was Zeid's immediate boss.

The UN rights chief recalled a man who was ever courageous and though direct in speech, never discourteous.

"Later, when I was an ambassador at the UN he inspired us, by being a dynamic and charismatic leader in his capacity as Secretary-General," Zeid continued.

"And most of all, he was a friend and counsel -- to me and to so many others. Whenever, as UN High Commissioner for Human Rights, I felt isolated and alone politically I would go for long walks with him around Geneva, and listen."

For Lise Kingo, CEO and Executive Director of the UN Global Compact, Annan is remembered as the visionary founder of her office, the world's largest corporate sustainability initiative.

As the world embarked on the new millennium, Annan inspired the world's top business leaders to join governments in lifting the poorest nations out of poverty by adopting a more responsible and sustainable approach to business, producing this office.

In creating the UN Global Compact, Annan asked corporate leaders to publicly commit to 10 principles based on UN agreements in the areas of human rights, labor, the environment and anti-corruption.

"Some 18 years later, the concept of corporate sustainability is firmly established," Kingo said. "More than 9,000 of the world's leading private sector chief executives have joined the UN Global Compact and are driving new approaches to help achieve the Sustainable Development Goals," in reference to the goals set in the UN's 2030 Agenda.

She said as a result of Annan's vision, the UN Global Compact is attracting new participants on a daily basis.

In addition, The Elders, an independent group of global leaders advocating peace and human rights where Annan was a founding member, expressed shock and sadness at his passing.

Annan assumed the chair of The Elders in May 2013 and had been holding the position until his death.

Gro Harlem Brundtland, deputy chair of The Elders, said "Kofi was a strong and inspiring presence to us all, and The Elders would not be where it is today without his leadership."

He pledged on the group's behalf to "continue to uphold his values and legacy into the future."

Annan was the seventh of nine men appointed secretary-general since the UN was established in 1945. He was the first to emerge from the ranks of UN staff and the second to come from the African continent.

Annan and the UN were jointly awarded the 2001 Nobel Peace Prize.