KABUL, Afghanistan - Two U.S. Navy service members disappeared in a dangerous area of eastern Afghanistan, prompting a massive air and ground search and appeals on local radio stations for their safe return, NATO and Afghan officials said Saturday.

The two left their compound in the Afghan capital, Kabul, in a vehicle Friday afternoon, but never returned, NATO said in a statement. Vehicles and helicopters were dispatched to search for the two, who may have been killed or captured by the Taliban in Charkh district of southern Logar province - about a two-hour drive south of Kabul, said district chief Samer Gul.

Elsewhere, five U.S. troops died in separate bombings in the south, setting July on course to become the deadliest month of the nearly 9-year war for Americans.

Rising casualties are eroding support for the war even as President Barack Obama has sent thousands of reinforcements to try to turn back the Taliban, who would have a leg up in the propaganda war with the capture of two U.S. troops.

A NATO official, speaking on condition of anonymity because of the sensitivity of search operations, confirmed the two were Navy personnel, but would not identify their unit to avoid jeopardizing search operations. The official said it was unclear what the two were doing or what would lead them to leave their compound. The official would not say whether the two were on official business.

The Taliban have not contacted the coalition force to claim responsibility or make any demands for their release, the official said.

Gul, the district chief in Charkh, said that a four-wheel drive armored sports utility vehicle was seen Friday night by a guard working for the district chief's office. The guard tried to flag down the vehicle, carrying a driver and a passenger, but it kept going, Gul said.

"They stopped in the main bazaar of Charkh district. The Taliban saw them in the bazaar," Gul said. "They didn't touch them in the bazaar, but notified other Taliban that a four-wheel vehicle was coming their way."

The second group of Taliban tried to stop the vehicle, but when it didn't, insurgents opened fire and the occupants in the vehicle shot back, he said.

NATO said a search is under way for the missing service members. According to Gul, one may have been killed and the other taken hostage by the Taliban.

"Maybe they wanted to go to Paktia province or to the American base, but they came down the wrong road toward Charkh," Gul said. "They didn't pay any attention to the police. Otherwise we could have kept them from going into an insecure area and now this unfortunate incident has happened."

The only U.S. service member known to be in Taliban captivity is Spc. Bowe Bergdahl of Hailey, Idaho, who disappeared June 30, 2009 in neighboring Paktika province, an area heavily infiltrated by the Haqqani network, which has deep links to al-Qaida. He has since appeared on videos posted on Taliban websites confirming his captivity.