It started with a tip. It ended with the fiercest firefight Afghanistan had seen in almost a year.

Interviews with U.S. commanders offer a picture of how troops on Monday stumbled into the battle in the mountains of southeastern Afghanistan, a confrontation in which more than 18 enemy fighters died.

It started Monday morning when a patrol of U.S. Special Forces soldiers and Afghan militia checked a mud-walled compound near the southeast town of Spinboldak. They had heard the building might be home to enemy activity.

Suddenly, bullets began whizzing. After the ensuing firefight, one rebel was killed, another injured and a third was captured. Under interrogation, the man gave up a blockbuster piece of intelligence.

In a nearby mountain, he said, they would find 80 armed men.

It took 26 minutes for Apache helicopters to scramble, said Lt. Col. Bob Ballew. Once they arrived, the Apaches were fired on by rocket-propelled grenades and small arms.

The lead aircraft returned fire and radioed for support. Within minutes, the Apaches would be joined by B-1 bombers, F-16 fighters flown by the Norwegian Air Force, AC-130 gunships and more Apaches.

The assault on Adi Ghar mountain had begun.

All night, the cave-pocked mountain was pummeled by bombs, some as large as 2,000 pounds. The gunships and helicopters dropped off soldiers and strafed enemy positions with rocket and cannon fire. It was the most intense battle in Afghanistan since Operation Anaconda, a fierce eight-day battle in March against Taliban and Al Qaeda holdouts in a different area of southeastern Afghanistan.

By dawn on Tuesday, at least 18 rebels had been killed. There were no reports of coalition casualties.

The mountain, about 15 miles northeast of Spinboldak, had been checked from the air but not investigated by ground troops, Ballew said. Enemy activity apparently hadn't been noticed.

"If you've spent time flying over this country or driving through it, it's pretty easy to see that there are all kinds of nooks and crannies," said Lt. Col. Michael Lerario, commander of the quick response team. "Until you actually get in there with infantrymen, you may not see all that's in there."

When the dust settled, however, it wasn't clear how many enemy were left. The U.S. military said it now doubted if there were more than the 18 rebels already killed, not 80. If there were, the military said, they would be nearby.

"They may have moved to other caves to try to escape us, or they may have tried to sneak off down the mountain," said Col. Roger King, spokesman for the U.S. military at the Bagram Air Base. "Either way, we will continue to hunt them."

Troops began checking the caves one by one — even though more rebels higher up the mountain might have been waiting. More than a hundred caves and many more shallow openings loomed in the rocky terrain as a hard rain began falling.

"Enemy contact or not, they had to go to the next step, which is to determine what's in the cave," said Lerario. "Is the cave being used for anything in particular? Does the cave present a threat?"

So far, a dozen caves have been investigated, yielding stashes of cooking oil, food, boots, blankets, lanterns, water, vitamins, mules and 107 mm rockets. Blood also was found, though no bodies have been discovered. Two men were detained.

The caves were apparently being used as a staging area or supply depot. U.S. soldiers maintain a large base in the southern city of Kandahar, about 90 miles west of Spinboldak. If there was a target, it remains unclear.

Who was occupying the caves is another matter. King points to one man: Gulbuddin Hekmatyar, a renegade southern warlord who has allegedly joined forces with Taliban and Al Qaeda sympathizers.

"The only indications that we have still point to a primary alliance to Gulbuddin Hekmatyar's group," King said. "But as we've said before, Hekmatyar himself has made statements that he's trying to align with Taliban remnants and Al Qaeda. So there's every possibility that these men may have seen themselves as being aligned with more than one group."

The United States remains the largest coalition force in Afghanistan, with about 8,000 soldiers stationed there. Britain, Poland, Italy, Canada, Spain, Norway and several other countries have sent troops to help with mine-clearing, construction and other tasks. Australia, Jordan, Germany and several Scandinavian countries also have at times placed special forces units in the country.

Kabul, the capital, is patrolled by an international peacekeeping force that includes troops from Austria, Belgium, Bulgaria, Great Britain, Denmark, Finland, France, Germany, Greece, Italy, the Netherlands, New Zealand, Norway, Portugal, Romania, Spain, Sweden, and Turkey.