U.S. Defense Secretary Robert Gates, meanwhile, arrived in Afghanistan's capital for meetings with President Hamid Karzai and top NATO commander Gen. David Petraeus.
Gates flew Thursday morning to Kabul from Baghdad, where he participated in ceremonies marking the formal close of the U.S. combat mission in Iraq. The Pentagon chief also plans to visit U.S. troops in Afghanistan.
NATO said one U.S. service member was killed in the country's east and the other in the south - regions where fighting between the coalition and Taliban insurgents has been at its most intense. No other details were given in keeping with standard NATO procedure.
The deaths bring to three the number of U.S. service members killed in September and follows a spike in casualties during the last two weeks of August that saw the monthly total rise to 55. The August figure was still below the back-to-back monthly records of 66 in July and 60 in June, although total U.S. combat deaths in January-August of this year - 316 - exceeded the previous annual record of 304 for the whole of 2009.
NATO said coalition forces beat back an attack on a combat outpost in Paktika province's Barmal district along the mountainous border with Pakistan, killing at least 20 insurgents. Defenders first returned fire with mortars and small arms before calling in an air assault, the alliance said in a statement, adding that no NATO or Afghan government forces were killed.
NATO also said it had killed or wounded as many as 12 insurgents, including two commanders, in an airstrike Thursday on a car traveling along back roads in northwestern Takhar province's Rustaq district.
However, the office of President Karzai, who has repeatedly warned that civilian casualties undermine anti-insurgency efforts, issued a statement condemning the attack, saying 10 campaign workers had instead been killed and two injured.
The alliance said it was aware of Karzai's claim and was investigating the incident.
Further east in Ghazni province's Andar district, five other insurgents were killed in an airstrike as they were placing a roadside bomb, NATO said. That followed an incident in nearby Khost province on Wednesday in which a suicide car bomber attempted to ram a coalition patrol, but managed only to set off his bomb's initiation device, killing himself but failing to detonate his explosives.
In volatile Helmand province to the south, coalition and Afghan forces killed 11 insurgents and captured four, including a regional Taliban shadow district governor, Mulla Sayed Gul, responsible for ordering attacks and dispensing funds, the provincial governor said.
NATO said it used another airstrike in Paktika to kill the leader of an insurgent cell responsible for laying roadside bombs and smuggling foreign fighters into the country. Ground forces dispatched to the site found weapons and bomb-making materials, it said. One other insurgent was killed and one detained after the ground force later moved in on a compound frequented by the Taliban commander, it said.
The commander was not identified by name and it wasn't clear how many fighters he controlled.
Paktika is one of several eastern provinces where the Taliban and their allies maintain cross-border routes to smuggle in weapons and militants, many of them linked to al-Qaida and recruited from their homelands in the Persian Gulf, North Africa and further afield.
Estimates of the number of foreign fighters in Afghanistan vary, with the vast majority of insurgents still drawn from Afghanistan's multitude of tribes, especially in the Pashtun-dominated south.
U.S. special operations forces have increasingly targeted Taliban field commanders as a means of attacking morale and discouraging other insurgents from taking on leadership positions, a strategy NATO hopes will turn the tide of the nearly nine-year war.
Also in Paktika, Afghan and coalition forces detained suspected insurgents linked to the Taliban-allied Haqqani Network in raids on compounds in Orgun district along the border with Pakistan on Tuesday and Wednesday nights, NATO said. The network is known for operating on both sides of the border and launched an assault on two U.S. bases last month that was repulsed with the loss of more than 30 insurgent lives.
Meanwhile, larger than usual crowds gathered to withdraw funds from Afghanistan's largest bank, but there was little sign that questions surrounding its viability had sparked a major panic.
Nervous customers flocked to Kabul Bank branches on Wednesday to take out their money following the resignation of two top bank executives amid allegations they mismanaged funds and spent money on risky real estate ventures.
On Thursday, the crowd at Kabul Bank's main branch in the center of the capital was only somewhat larger than normal, following government efforts to reassure the public. Afghan television stations broadcast remarks Wednesday by central bank Gov. Abdul Qadir Fitrat insisting that Kabul Bank was solvent and had enough liquidity to meet demands.
Problems at the bank could have wide-ranging political repercussions since it handles the pay for Afghan teachers, soldiers and police in the unstable, impoverished nation beset by the stubborn Taliban insurgency and widespread drug trafficking and plundering of aid money.
The bank's woes also tie into the web of corruption and personal connections that has soured many Afghans on their government. President Karzai's brother, Mahmood Karzai, is the bank's third-largest shareholder with 7 percent.
The Finance Ministry on Thursday issued a statement assuring government employees that they would continue to be able to deposit and withdraw their salaries at Kabul Bank, and said the replacement of the top executives aimed to improve management and services and was "part of the life cycle of a business."
"The Ministry of Finance has confidence in the Kabul Bank's ability to facilitate banking transactions, including salary disbursement," the ministry said.