Image caption Ban Ki-moon's term as head of the global body is due to expire at the end of 2011

Ban Ki-moon has formally announced his candidacy for a second five-year term as UN secretary general.

Mr Ban pledged to keep leading the world body as a "bridge-builder" in a time of unprecedented global change.

With no rival for the post, the former South Korean foreign minister is almost certain to be re-elected.

From the beginning Mr Ban has presented himself as a man of quiet diplomacy, which set him apart from his outspoken predecessor Kofi Annan.

'Low-profile'

At Monday's news conference in New York, Mr Ban said: "It has been an enormous privilege to lead this great organisation.

"If supported by the member states, I would be deeply honoured to serve once more, throughout my time in office, I have sought to be a bridge-builder."

Powerful nations in the Security Council seemed to want a low-profile leader after the schisms of the 2003 Iraq war.

Mr Ban, who took the job in 2007, was criticised though for being too deferential to these powers and for being too timid to confront the world's worst human rights abusers.

But Mr Ban insisted again on Monday that he had spoken out strongly for human rights - and he has won praise recently for supporting Arab pro-democracy demonstrators.

He told journalists his accomplishments included overseeing swift responses to a series of humanitarian crises, and pushing to make climate change a top concern of world governments.

Mr Ban has already won public endorsement from France and China, and diplomats expect his re-election process to be over by the end of the month.