Funeral services have been held in the northwestern U.S. state of Washington for the Army Special Forces soldier killed last week in Afghanistan. He was the first American soldier killed by hostile fire in the war.

A Pentagon spokesman initially suggested that Sergeant First Class Nathan Chapman may have been killed in a pre-arranged ambush, perhaps betrayed by Afghan tribal leaders near the border with Pakistan.

But General Richard Myers, Chairman of the military's Joint Chiefs of Staff, later played down the notion of a set-up. "First of all, I'm going to avoid characterizing that situation with those kind of words," he said. "I mean, we just don't know yet."

General Myers indicated the incident, in which a Central Intelligence Agency operative was wounded, may have simply been a reflection of the dangerous, lawless conditions in Afghanistan, conditions U.S. teams on the ground are aware of. "They understand the situation on the ground. They understand how dangerous that is," he said. "I don't know how many times we've stood up here [at the Pentagon] and said this is a dangerous place, that allegiances sometimes change and that you've got to be very, very careful. And our people on the ground are probably some of the smartest in that regard."

General Myers went on to say rather than speculate about what happened, reporters should wait for the results of an investigation into the incident.

But government officials now say there is no formal investigation in the sense of a criminal-type police probe into the shooting.

Some sources suggest this may be because the team Sergeant Chapman was with was not a typical Army Special Forces team but actually a Central Intelligence Agency paramilitary group. He was apparently attached to it as its communications specialist.

The Central Intelligence Agency will not comment on any aspect of the incident, in which officials originally suggested Sergeant Chapman was shot and killed and the CIA agent wounded immediately after leaving a meeting with tribal elders in an Afghan village.

But now defense sources say the shooting occurred several kilometers away while the victims along with at least one other CIA operative and several Afghan fighters were travelling in a vehicle.

The sources say the group returned fire before speeding off.

Forces who later scoured the incident area found no bodies, indicating the assailants escaped. It remains unclear whether they were bandits, al-Qaida terrorists or Taleban fighters.