KABUL, Afghanistan — Like hundreds of thousands of Afghan men, he volunteered in the national army, ran drills in the mud, carried an automatic rifle, and worked alongside coalition mentors struggling against a hardcore insurgency.
But he was not one of them.
On Saturday, he walked into a meeting of NATO trainers and Afghan troops at Forward Operating Base Gamberi in the eastern province of Laghman and detonated a vest of explosives hidden underneath his uniform.
Five NATO troopers, four Afghan soldiers and an interpreter were killed in the deadliest sleeper agent assault.
Four Afghan soldiers and three interpreters were wounded in Saturday's attack.
The Taliban claimed responsibility for the bombing and said the soldier was a sleeper agent who joined the army a month ago, a contention confirmed by an Afghan army official.
"Today, when there was a meeting going on between Afghan and foreign soldiers, he used the opportunity to carry out the attack," Taliban spokesman Zabiullah Mujahid said in an email to reporters.
Attacks by insurgents donning security uniforms are a relatively rare but recurrent problem as NATO and Afghan forces work more closely together. Afghanistan's security forces are also ramping up recruitment of Afghan soldiers and policemen so they can take the lead in securing their nation by the end of 2014, adding more than 70,000 police and soldiers last year in an effort to reach 305,000 troopers by the end of this year.
Afghan security forces are supposed to be vetted by past employers or even village elders, but in a country where unemployment is about 35 percent, the literacy rate is about 28 percent, and computerized record-keeping is a novelty, background checks are often rudimentary.
The explosion took place at 7:30 a.m., as many people on the base were beginning the morning shift and as NATO and Afghan service members conducted what military officials call a "key leader engagement" meeting, according to a NATO spokesman.
After the explosion, Blackhawk helicopters swooped down to carry the dead and wounded to hospitals.
Baz Mohammad Sherzad, the director for health in nearby Nangarhar province, said the bodies of four Afghan soldiers brought to a hospital in Jalalabad were too badly damaged to determine their military rank.
NATO declined to provide further identifying information about its soldiers killed in the blast, pending notification of their next of kin.
In the wake of such attacks, often it's not clear whether the shooter was an Afghan trooper who turned on his Western counterparts spontaneously or an insurgent who donned a uniform to infiltrate the base and attack from inside.
On Friday, a suicide bomber dressed as a policeman blew himself up inside the Kandahar police headquarters complex, killing the top law enforcement officer in the restive southern province.
Saturday's funeral for police chief Khan Mohammad Mujahid, one of Afghanistan's most prominent law enforcement officials, was attended by at least 1,500 people, including Kandahar's governor, the Afghan interior minister and the Afghan president's half brother, Ahmad Wali Karzai.
Earlier this month, a man wearing an Afghan border police uniform shot dead two American military personnel tasked with helping train members of the country's security forces in Faryab province.
In February, an Afghan soldier shot and killed three German soldiers and wounded six others in the northern province of Baghlan.
Until Saturday, the worse case of a sleeper agent attack was in November, when an Afghan border policeman shot to death six American soldiers before he himself was shot to death in the eastern province of Nangahar. The policeman had been in the force for three years and had accompanied American troopers for about three months when he opened fire on them.
The Taliban took responsibility for that attack.