Kabul, Afghanistan ? Thousands of ethnic Pashtuns are fleeing northern Afghanistan, claiming that anti-Taliban commanders have been inciting people to loot their homes and in some cases, kill Pashtuns, a U.N. spokesman said Thursday.

Meanwhile, a French aid organization issued an urgent appeal for more food aid in northern Afghanistan.

In recent days about 20,000 Afghans, mostly people fleeing drought, hunger and ethnic strife, have fled to Chaman, a crossing point on the Afghan-Pakistani border, said U.N. spokesman Yusuf Hassan said.

“It is a very disturbing picture of gross human rights violations,” he said. Hassan did not give a breakdown of how many were fleeing ethnic tensions and how many were seeking food.

The Taliban, who were ousted from power last year, were dominated by Pashtuns, Afghanistan’s largest ethnic group in Afghanistan. The U.S.-backed northern alliance was largely Tajik and Uzbek.

The reports add to concerns that post-Taliban Afghanistan may be unable to rein in the ethnic, tribal and personal rivalries that have riveted the Central Asian nation for more than two decades.

People fleeing northern Afghanistan “say that commanders in those areas are instigating the locals to rob them and kill and harass the Pashtun population,” Hassan said.

The United Nations has complained to the interim government, Hassan said, but “many of those areas are areas where there is no national authority.”

Large parts of Afghanistan are controlled by local warlords. The national government has no army.

A U.S. official said Thursday that the Central Intelligence Agency is warning in a classified analysis that Afghanistan could descend into civil war because of fierce competition for power among rival warlords.

There is agreement within the U.S. government that the country’s security could be bolstered by setting up an Afghan army, a national police force and an effective legal system.

But there is disagreement within the U.S. government over whether to expand an international peacekeeping force, said the official, speaking on condition of anonymity. He said the State Department favored the expansion but the Pentagon was reluctant to take that step.

Britain leads a 4,500-member international force and has the largest contingent of peacekeepers.

Hardly a day goes by without another reminder of the country’s volatile peace.

Gunmen opened fire on a British patrol in the Afghan capital of Kabul and the British returned fire, a peacekeepers’ spokesman said Thursday. It was the second such incident in less than a week.

There were no immediate reports of casualties on either side as a result of the brief exchange of gunfire Wednesday night between British peacekeepers and local Afghans, said Jonathan Turner, a spokesman for the British-led peacekeeping force.

“They had just stopped their vehicles when they were fired upon,” he said.

Last Saturday, members of the same British regiment opened fire on an Afghan car that witnesses say was carrying a pregnant woman. The peacekeepers said they heard gunfire and fired in response. Afghan witnesses say the shooting, which killed a local man, was unprovoked.

The French non-governmental organization Doctors Without Borders issued an urgent appeal Thursday for more food aid in remote areas of northern Afghanistan.

A statement from the group described dire conditions at a displaced persons camp in northern Faryab province, where it said mortality rates, malnutrition and the number of internally displaced people are rising sharply.

“In northern Afghanistan, a new disaster is in the making and can only be averted by immediate and unrestrained action,” said the group’s operational director, Christopher Stokes.

Also Thursday, U.S. military officials took a group of elders from the southern province of Kandahar, including the province’s governor, on a tour of a U.S.-controlled airport to prove the runways were too bomb damaged to allow for flights of would-be Islamic pilgrims to Saudi Arabia for the annual hajj pilgrimage.

More than 4,000 Kandahar residents had each paid $1,600 for government hajj packages, only to be told the airport was unusable for large passenger planes.

Ibrahim Khalil Xar, who identified himself as a doctor in Kandahar participating in Thursday’s tour, said the elders were satisfied that the United States was telling the truth about the runway.

The government’s inability to transport all pilgrims to the hajj came to the forefront last week when the civil aviation minister was slain at Kabul airport.

Interim Prime Minister Hamid Karzai blamed the death of the minister, Abdul Rahman, on a personal feud within his administration.

On Wednesday, however, Foreign Minister Abdullah publicly discounted those claims, saying Rahman was killed by a crowd of would-be Islamic pilgrims angry over flight delays to Saudi Arabia.

In an apparent attempt to play down reports of division within his government, Karzai told Associated Press Television News on Thursday that he and the rest of the Cabinet back the foreign minister’s position.

However, he did not back away from his initial claim that someone was behind the killing.

“The investigation is going on. We know who did it,” he said. There was no explanation for the apparent contradiction.