The international community has made progress in easing the humanitarian crisis in Darfur, but those efforts could unravel because of the "total failure" to bring lasting security to the Sudanese region, the top U.N. refugee official said Tuesday.

U.N. High Commissioner for Refugees Antonio Guterres' assessment came as he took stock of the refugee situation in Sudan and

Iraq ¡ª two of the world's biggest refugee challenges.

Guterres, who recently returned from Darfur, applauded gains made in Sudan on the humanitarian front, saying the U.N. had assisted in the return of 30,000 refugees there in the first four months of the year, a figure that trumped repatriation levels for all of 2006.

But for that level to be sustainable, security must be realized in the region, and this can only be accomplished through a comprehensive and effective peace agreement, Guterres said.

"It is crucial ... for the international community to be fully engaged in putting pressure for a comprehensive, effective peace agreement to be established as quickly as possible, involving all the parties," Guterres told reporters, arguing that not enough attention has been paid to ongoing negotiations.

The United Nations has been pushing hard to end the four-year conflict in Darfur, where more than 200,000 people have died and 2.5 million displaced in fighting between ethnic African rebels and government forces and their allied Arab militia, known as the janjaweed.

Attempts to broker peace have largely failed, with forces on both sides accused of abuses.

An agreement was signed last year between the government and one rebel group, but other rebel factions and refugees have rejected the deal.

"If there has been a very important success ... in humanitarian relief, I think there has been a total failure in relation to protection and security," Guterres said.

A 7,000-strong African Union peacekeeping force has been in place in Darfur since 2004, but it is ill-equipped and understaffed to do the job of patrolling the region, which is the size of France. Khartoum has recently agreed to allow 3,000 U.N. peacekeepers enter the region to reinforce the AU force after months of stalling.

But Guterres warned that, "even with a meaningful international force, it is always very difficult to guarantee security if the political background ¡ª based on a comprehensive peace agreement ¡ª is not established."

On Tuesday, the U.N. said six UNHCR members were briefly kidnapped in Darfur by an unknown rebel group and their vehicles hijacked. The workers were found unharmed several hours later, after being dropped off by the kidnappers.

In the case of Iraqi refugees, Guterres said some pivotal steps were taken last month during a conference in Geneva, which resulted in pledges from countries not to forcibly repatriate Iraqis fleeing their homeland.

Iraq's commitment to support refugees outside its borders, including a pledge of $25 million, was also "extremely important," he said. Of the roughly 2 million Iraqis who have fled the country, the overwhelming majority are in

Syria and Jordan, with the influx straining those countries' social and economic infrastructures.

The Iraqi government has insisted that the 2 million refugees abroad and 1.9 million who have fled to other parts of Iraq will eventually return to their homes.

Guterres said his agency was raising the number of refugee referrals to 20,000 per year, out of the total global capacity of 50,000 to 70,000 for all refugees.

To date, the agency has referred for consideration more than 3,900 refugees to various nations, including 2,934 to the United States, he said. The U.S. has said it would accept referrals for 7,000 refugees by the end of June ¡ª up from only about 200 in 2006 ¡ª with the possibility of increasing that number later in the year.