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 after getting lost in Charkh district of southern Logar province, said district chief Samer Gul.
Elsewhere Saturday, 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.
New York Times reporter David Rohde was also kidnapped in Logar province while trying to make contact with a Taliban commander. He and an Afghan colleague escaped in June 2009 after seven months in captivity, most of it spent in Taliban sanctuaries in Pakistan.
Mohammad Nasir Medaruz, director of a radio station in Logar called Meli Pegham, or "National Message," said he had received a phone call from coalition officials asking that he broadcast a message offering $10,000 for information about the whereabouts of each missing service member.
"I told them that Logar is not a safe area and if I broadcast that, I could get attacked," Medaruz said.
He said that if the military officials paid him, he would broadcast the information and say that it was an "advertisement."
He said he did not broadcast the information, but another radio station, sponsored by the military in Logar, did air the message.
On Saturday in the same district in Logar, the manager of an Afghan construction company and his driver were kidnapped, according to Din Mohammad Darwesh, spokesman for the governor of Logar province. The two Afghans captured worked with Afghan Korean Construction Co., he said.
The five American troops died in roadside bombings in the south - four in a single blast. A fifth service member was killed in a separate attack in the south where international forces are stepping up the fight against the insurgents.
The latest deaths brought to 75 the number of international troops killed in Afghanistan this month, including 56 Americans. Many of the deaths have occurred in the south where Afghan and NATO forces are ramping up operations against the Taliban in their southern strongholds, hoping to enable the Afghan government to expand its control in the volatile region.
On Tuesday, an international conference in Kabul endorsed President Hamid Karzai's plan for Afghan security forces to assume responsibility for protecting the country by the end of 2014. Obama has pledged to begin removing U.S. troops starting in July 2011, although he has linked the drawdown to security conditions on the ground.
Associated Press Writer Rahim Faiez in Kabul contributed to this report.