The UN-led tsunami relief efforts and its involvement in rebuilding Iraq demonstrate the UN's central role in a wide range of matters, the Secretary-General wrote in an opinion piece published in the Wall Street Journal Wednesday.

The article comes a day after Ruud Lubbers, who resigned as United Nations High Commissioner for Refugees following allegations of sexual harassment, claimed he took the step to help Annan.

The 65-year old former Prime Minister of the Netherlands stepped down amid press coverage of a previously internal UN report on sexual harassment charges brought against him by a female UNHCR staffer over an incident which took place in December, 2003.

That report, by the UN Office for Internal Oversight Services (OIOS), was presented in July, 2004, to Annan, who decided that the complaint could not be sustained by the evidence.

On Friday, after The Independent published details of the report, Annan met with Lubbers in New York. Speaking to reporters afterward, the High Commissioner maintained his innocence and said he would not resign.

But two days later, he tendered his resignation, which was accepted by the Secretary-General as an opportunity for UNHCR to make a fresh start.

"My decision to resign has much to do with my wish not to complicate life for the Secretary-General, who is facing a series of problems and ongoing pressure from the media," he wrote in a letter sent to 6,000 UNHCR staff spread over 115 countries yesterday.

"I regret the sudden news and would have preferred to deliver it another way. Let me assure you I did not take this decision lightly," Lubbers told staff.

In his resignation letter to Annan, Lubbers said he felt that "despite all my loyalty, insult has now been added to injury".

Annan, in his article acknowledged the UN's imperfections and stressed the efforts he has made over the eight years of his term to improve and strengthen the organization.

He also stressed that the UN could not expect to survive into the 21st century unless ordinary people throughout the world felt that it did something for them.

"In recent years, bitter experience has taught us that a world in which whole countries are left prey to misgovernment and destitution is not safe for anyone," he wrote.