UNITED NATIONS – The top U.N. envoy to Sudan said yesterday the Sudanese government has failed to improve security for the embattled people in Darfur or brought to justice the perpetrators of atrocities during the 19-month conflict.

Jan Pronk accused the government and rebels of continuing to violate an April cease-fire, with the army attacking, sometimes with helicopter gun ships and the rebels often directing their fire at police. But he said “there are signs of improvement on the political front.”

In an open briefing to the U.N. Security Council on two reports by the secretary-general, Kofi Annan, Mr. Pronk called for a beefed-up African Union force with a greatly expanded mandate “in the coming weeks.”

“It can help to protect the people by being present over a wide area, by being seen, by acting as a deterrent,” he said.

Mr. Pronk reiterated that the conflict in the western Sudanese region of Darfur, which has killed over 50,000 people and forced 1.4 million to flee, is “the worst humanitarian crisis of today.”

He warned that failure to resolve it “could create the conditions for a widening regional or even global confrontation,” and called for progress in separate political talks this month on Darfur and on ending the 21-year civil war in southern Sudan.

Sudan’s Arab-dominated government is accused of mobilizing Arab tribal fighters for attacks on Darfur’s villagers, in retaliation for uprisings launched by two non-Arab Darfur rebel movements in February 2003. Sudan denies any responsibility and says it has disarmed some of the Arab militiamen, known as Janjaweed.

Calling for “a comprehensive political solution” in Sudan, Mr. Pronk said agreements already negotiated to resolve the war in the south should be used as the basis to solve conflicts in Darfur and elsewhere in the country.

He urged the international community to put pressure on Sudan to change its policies and bring into the political process rebel movements, tribal leaders, opposition groups, civil society, women’s groups, and the younger generation that will have to build a new Sudan.

“Aim not at regime change but at regime character change,” Mr. Pronk told the 15-member council and an audience from many nations.