A top United Nations official, Sergio Vieira de Mello from Brazil, has taken over from Mary Robinson as head of the UN's Human Rights Commission.

My immediate priorities are... protection of civilian populations in conflicts, combating racism, the rights of women

Sergio Vieira de Mello

Mrs Robinson's five years in the world's top human rights job has sometimes been marked by controversy.

She fell foul of the United States when she suggested that the war against terrorism might be undermining human rights standards.

In contrast, the appointment of Mr de Mello has been welcomed by the US, but some human rights groups fear he may lack the political experience necessary for the job.

Uneasy position

Mr de Mello himself has described the post as a "political minefield", and the BBC's Imogen Foulkes in Berne says he has certainly taken over one of the most difficult and delicate jobs in the UN.

Robinson: Unafraid to speak her mind on human rights issues

The human rights commissioner is supposed to condemn human rights abuses wherever and whenever they occur.

But in practice it is not so easy, as Mrs Robinson found out.

Our correspondent says the world will unite to condemn human rights abuses should they take place in small and powerless nations, but criticise one of the big powers and the human rights commissioner is accused of meddling.

The US-based Human Rights Watch group said: "The new high commissioner must show strong and principled leadership at a time [when] the UN human rights system and international law are under attack."

During her time in office, Mrs Robinson managed to irritate the US, Russia and China with her comments on their human rights records.

Her successor is thought to have a less out-spoken style.

'Reviewing priorities'

Mr de Mello's appointment has been warmly welcomed by the US where Mrs Robinson's departure seems to be something of a relief.

De Mello aided East Timor in its bid for independence

Speaking publicly for the first time as UN high commissioner, 54-year-old Mr de Mello said his aims were threefold.

"My immediate priorities are broad things like protection of civilian populations in conflicts, combating racism, the rights of women," he told reporters in his new office in Geneva.

"Those are the three huge chapters that require a lot of attention in addition to all geographical hotspots that are already well known."

However, he also said he needed to "review my priorities before I speak to governments".

Field experience

Mr de Mello is no stranger to the campaign against human rights abuses.

He has spent more than 30 years in the field working for various UN agencies.

He has been posted to Sudan, Mozambique, Peru, Kosovo and earlier this year served as UN administrator for East Timor where he guided the new nation to independence from Indonesia.

UN Secretary General Kofi Annan said Mr de Mello's work in East Timor had been brilliant.

But some human rights groups fear the new commissioner's long experience in the field may not equip him for the political challenges he will face at UN headquarters in Geneva and New York.

Upholding human rights the world over - and judging each nation by the same standards - is likely to be Mr de Mello's most difficult task.