KABUL (AFP) –
A senior NATO commander in Afghanistan conceded on Wednesday for the first time that civilians may have been killed during a joint military operation with Afghan forces in the east of the country this week.

"There is confusion. The initial reports are confusing like always in this situation. In the confusion there was obviously a fire-fight and we are investigating," Lieutenant General David Rodriguez told journalists.

"There could possibly have been some civilians killed," added Rodriguez, the number two commander of NATO troops serving in Afghanistan.

President Hamid Karzai's office said six civilians, including a woman, died when troops from the NATO-led International Security Assistance Force (ISAF) conducted an operation in the eastern province of Laghman.

Several other people were detained, officials have said.

ISAF said previously it had no reports to substantiate claims of civilian casualties during the joint Afghan-international operation in Laghman. The government says it is investigating the incident in conjunction with ISAF.

Hundreds of students took to the streets in the eastern town of Jalalabad on Wednesday shouting "death to America" to protest against the alleged deaths of civilians during a NATO-led raid, witnesses said.

Most of the roughly 400 demonstrators were university students and blocked a key highway to the capital Kabul.

The protesters also demanded the release of those arrested and a classmate detained last month in his home province of Paktia, also in the east.

Civilian casualties are highly sensitive in Afghanistan where officials say it creates animosity against the Western-backed government, and 113,000 NATO and US forces fighting against an escalating Taliban insurgency.

Karzai has long called on foreign troops to avoid civilian casualties during operations against insurgents.

US Defence Secretary Robert Gates, currently visiting Afghanistan, said Tuesday that preventing civilian deaths would be a "top priority" as Washington and NATO allies prepare to boost the overall number of troops to 150,000.