As the searing sun rises over the desert landscape of Sudan's troubled Darfur region, officers from about a dozen African countries gather inside a cramped canvas tent near the town of Nyala for their morning ritual of security briefings and daily assignments.

At first, several junior officers grumble about their orders - to patrol a lawless displaced-persons camp overflowing with 90,000 people. Amid rising insecurity in Darfur, even routine patrols have become dangerous. But the ranking officer of this African Union force, a beefy Nigerian named Olusegou Adeleke, cuts them short. "The mandate of the protection force is simply to protect, whether with a pen knife or with stones," he barks. "And protection must be given."

Since its inception in 2004, the African Union's mission to Darfur has been a major test of Africa's collective ability to defuse its own conflicts and protect its civilians. Now amid talk of a United Nations force replacing the AU in Darfur - and, separately, of the AU deploying to Congo to disarm a stubborn rebel group - there's growing focus on how effective the AU's Darfur mission has been, and on what that portends for future AU efforts.

The final verdict isn't in, but it's clear AU troops are struggling often in vain to calm Darfur, a region the size of Texas where attacks by government-backed Arab militias began in 2003 against indigenous-African villages.

"In some ways as an institution [the AU is] still on [its] shakedown cruise," says a senior western diplomat in Abuja, Nigeria, observing AU-sponsored talks between Darfur's warring parties. He's referring to test voyages on which crews familiarize themselves with newly commissioned ships.

The 6,700 AU troops aren't even actually peacekeepers. Their limited mandate, as negotiated with Sudan's wary government, charges them only with monitoring and reporting violations of a much-abused year-old cease-fire between Sudanese troops and Darfur rebel groups, which rose up against the government citing economic marginalization.

AU troops are only allowed to use force to protect themselves - or civilians in their immediate vicinity. Most experts agree that this limited mandate severely hampers their ability to secure the area.

The AU is also faced with internal battles between rebel groups and growing numbers of bandits, all creating a general lawlessness and confusion in Darfur. In October, four AU soldiers from Nigeria and two contractors were killed. An investigation is still pending, but a monitor who asked to remain anonymous says the rebel Sudan Liberation Army is likely to blame.

"This peacekeeping mission is unique. I've been in Bosnia where there were lines of separation, but here there is nothing like that. Here there is no separation, rules, lines, clear zone of occupation," says an exasperated Colonel Vitalis Ajumbo, a Kenyan who oversees one of the region's more-volatile sectors.

Last week, the UN grounded some helicopters, because a renegade rebel group threatened to shoot them down. "Our humanitarian efforts are being destroyed on the ground," said UN spokeswoman Radhia Achouri.

Now a joint AU, UN, US, and European Union team is in Darfur assessing the feasibility of a UN force in Darfur. But even if the UN takes over, it may be next September before its troops are deployed.

Col. Ajumbo sees no need for a UN presence: "What is required is sincerity on the part of the parties. All we need is the logistics support and we will do it. We need firepower, manpower."

Mohammad Shorba, a commander with the rebel SLA, disagrees: "The AU is very weak. I'd like to see the UN take over for the AU as soon as possible. They have been here for over a year and failed to stop the violence. We ask the UN to come here urgently."

Theirs is part of a larger debate about whether blue-helmeted UN troops would be more effective in Darfur and elsewhere. An AU team recently investigated the possible deployment of 7,000 AU troops in eastern Congo with the aim of disarming a rebel group that goes by its French acronym FDLR, which continues to cause much trouble in the region. Already the UN has troops in the area - but they've been unable or unwilling to disarm the FDLR.

"The UN is no panacea," warns the western diplomat, citing mixed results of its peacekeeping in Congo and elsewhere. Furthermore, in Darfur, it's not entirely clear the Sudanese government will allow non-African UN troops into its country.

Another difference: The AU funds its missions via irregular handouts from the US, EU, and others, while the UN has a more-formal funding structure. This, and the UN's generally more-established peacekeeping system, could help bring more resources to bear in Darfur.

The AU does have significant limitations. Its communications system is rudimentary, for instance. Since there's virtually no cellphone or land-line service in Darfur, the AU essentially relies on rebels - or aid groups - to report attacks.

But the AU mission has seen limited success. It now provides patrols, with Sudanese police, for women in some of the many displacement camps scattered across Darfur. Walking up to 12 miles searching for firewood, many women have been attacked and raped. Such attacks have lessened since the "firewood patrols" began, but they still continue.

Ultimately what's needed is a political, not a military solution, experts say. Currently, "There is no peace to keep," says Eltayeb Ateya, a peace-studies expert at the University of Khartoum. "Someone is standing in the desert with a gun and asking, 'Who should I protect?' Everybody is fighting everybody."

• Wire services were used in this report.