SADAY KANDOW PASS, Afghanistan -- In the rocky hills of southeastern Afghanistan, America's allies in the fight against terrorism are at war against each other -- battling for supremacy over an area where al-Qaida and the Taliban are still hiding.

Up to 50 people have been reported killed and wounded since fighting erupted again Sunday in Khost province between forces of Bacha Khan Zadran -- a warlord who has worked with U.S. special forces -- and those of the governor appointed by Afghanistan's pro-U.S. president, Hamid Karzai.

Tensions between Zadran and Karzai's allies have been festering for months, sometimes prompting sporadic fighting.

The province, which borders Pakistan, is one of the key fronts in the war against terrorism, and the United States has been working with both of the rivals in the hunt for al-Qaida and Taliban holdouts.

But the clashes underscore the difficulties of the U.S. strategy of trying to forge alliances with Afghan fighters so to avoid committing large numbers of U.S. troops to the area.

Navigating among the factions is complicated by Afghanistan's ancient tribal feuds, complex ethnic loyalties and unfamiliar codes of conduct and honor.

Afghans here believe the Americans inadvertently triggered the weekend upsurge in fighting when Lt. Gen. Dan K. McNeill, the commander of U.S. forces in Afghanistan, met Zadran on Sunday.

The meeting was held so McNeill could demand that Zadran dismantle checkpoints that were interfering with coalition military movements. But rumors swept through the region that the Americans had arrested Zadran.

That prompted Gov. Hakim Taniwal's fighters, hoping to take advantage of the situation, to attack Zadran's militiamen in Khost city, the provincial capital. They drove Zadran's fighters from the Customs House, several municipal buildings and one of their main bases. Several of Zadran's fighters were killed.

"Many of my friends were killed then. We didn't start the fight. They thought Bacha Khan had been arrested by the Americans and moved against us," a Zadran fighter, Bahadar Khan, said.

In a mud hut at the top of Saday Kandow Pass outside the city, Zadran's fighters talked Tuesday of an impending, all-out assault on Khost city.

"We are on all sides. We have them surrounded. But right now, we are in a defensive position," Bahadar Khan said.

The governor's aides, however, insisted their forces were in full control of Khost city and had gained the upper hand.

The Americans are caught in the middle. They maintain two bases in southeastern Afghanistan -- one in Khost and another in Gardez.

Both U.S. compounds have been rocketed periodically and U.S. vehicles fired upon.