Four Arab detainees described by a U.S. official as "dangerous enemy combatants" slipped out of the fortress-like U.S. military prison at Bagram air base before dawn Monday, sparking a massive manhunt in the surrounding area by U.S. and Afghan forces, according to officials from both countries.

Also on Monday, U.S. military officials announced that American forces had located the body of the last of four Navy SEALs missing since a June 28 firefight with insurgents in northeastern Konar province.

Officials said that the commando appeared to have died of wounds suffered in the battle and that there was no evidence to support claims by a purported Taliban spokesman that fighters from the Islamic militia had captured and beheaded him.

The news followed a weekend of continued violence by insurgents suspected of links to the ousted Taliban rulers. Since April, the fighters have pursued a campaign of bombings and assassinations in a bid to disrupt parliamentary elections scheduled for Sept. 18.

The latest attacks include the beheading of at least six border police officers captured in an ambush in southern Helmand province Saturday and the killing of a prominent pro-government cleric, Maulvi Sayed Agha, and his wife by unknown assailants who broke into the couple's home in eastern Paktika province early Saturday.

In addition, a roadside mine explosion killed a dozen Afghan security officers Sunday in Paktia province, also in the east, according to Afghan officials.

The four escapees from the Bagram detention center, on a sprawling military base 35 miles north of the capital, were Arab nationals from Syria, Saudi Arabia, Kuwait and Libya, according to a high-ranking Afghan police official in Parwan province, where the base is located. It was the first known escape from the prison.

The official, who spoke on condition of anonymity, expressed amazement that the detainees, who are given only orange jumpsuits to wear, were able to break out of the heavily guarded detention center inside a base occupied by thousands of armed soldiers, dotted with minefields and surrounded by barriers and checkpoints.

"Even if those Arabs had wings, they should not have been able to escape," he said.

Lt. Col. Jerry O'Hara, a U.S. military spokesman, said the detainees were "dangerous enemy combatants." He said he could not comment further on who they were or how they might have gotten out of the prison, which houses between 450 and 500 inmates.

"We're treating this as a very serious incident and using all available assets to find these thugs," O'Hara said. "The reason these guys were in the facility is because they were a danger to society in general and Afghans in particular. . . . These guys are potential killers."

O'Hara said there were no indications that foreign or Afghan forces had been harmed during the escape. He said military officials believed the escapees were probably still on the base, where hundreds of Afghans work as laborers or drivers. All are screened and searched each time they enter or leave.

Nonetheless, a large contingent of U.S. and Afghan forces fanned out across the roughly dozen villages on the open plain surrounding the base, setting up checkpoints, distributing photographs of the wanted men and circling in helicopters, U.S. and Afghan officials said. The search continued late into Monday night.

O'Hara said U.S. troops were not conducting house-to-house searches. The Afghan police official, however, said they were doing so, or were at least planning to, and he expressed concern that this could alienate local residents.

"It will give the United States a bad name for a long time to come," the official said.

Since U.S.-led forces ousted Afghanistan's Taliban rulers in late 2001, the facility at Bagram has served as the U.S. military's main holding center for suspected Islamic rebels in the country, including alleged al Qaeda leaders captured outside Afghanistan and hundreds of detainees later sent to the U.S. military prison at Guantanamo Bay, Cuba.

Human rights groups have accused U.S. soldiers at the Bagram prison of torturing detainees and, in two cases, in 2002, killing them. Several U.S. soldiers are facing charges in connection with the deaths.

Over the past several months, U.S. military officials have been occasionally freeing batches of Afghan detainees from Bagram as part of an effort to encourage Taliban guerrillas to lay down their arms. On Saturday, a group of 76 was released.

The tense mood at Bagram on Monday was mixed with sadness over the confirmation that the last Navy SEAL missing in the rugged hills of Konar province was dead, O'Hara said.

"It's kind of bittersweet," he said. "We are severely disappointed that we didn't find him alive, but we are also relieved at the fact that he's no longer lost up in those mountains."

Only one member of the four-man SEAL reconnaissance team, which U.S. military officials said was hunting al Qaeda fighters as part of a wider operation, survived the June 28 battle. He was rescued July 3. The bodies of two others were found the following day.

A Special Operations helicopter sent to rescue the team when it came under fire was apparently hit by a rocket-propelled grenade and crashed into a mountainside, according to military officials. All 16 service members on board were killed in the worst American combat loss since the U.S. entry into Afghanistan in late 2001.

The SEAL commando located Sunday, whose name was not released pending notification of his family, was found near the helicopter crash site in an area that had been searched before but was difficult to survey because of high peaks and heavy tree cover, O'Hara said.

An Afghan's car is inspected at a U.S. military checkpoint near the Bagram air base after four Arabs, described by a U.S. spokesman as "dangerous enemy combatants," made the first known escape from the prison on the base. Kabir Ahmad, chief of the Bagram district, displays a leaflet with photographs of the four prison escapees, who are from Syria, Saudi Arabia, Kuwait and Libya.