KABUL, Sept 23 (Reuters) - NATO-led and Afghan forces are investigating whether four people they killed in eastern Afghanistan were Taliban rebels, members of the Afghan security forces or civilians, a spokesman said on Sunday.

The issue of civilian casualties is a sensitive one. Afghan leaders have accused foreign forces operating in the country of not taking enough care to verify their targets before opening fire, particularly when using air power.

The two main foreign forces in Afghanistan, the NATO-led International Security Assistance Force (ISAF) and the U.S.-led coalition, both say they take extreme care to avoid civilian casualties and blame the Taliban for operating among the people.

Afghan and ISAF troops called in air support after an Afghan army base in the Sarkani district of the eastern province of Kunar came under rocket attack on Saturday, an ISAF statement said.

ISAF helicopters identified a group of 30 suspected insurgents at the place where they believed the rockets were fired from and attacked them, killing four and wounding 12 others.

But initial reports suggested the suspected insurgents were in fact Afghan police or armed road construction security guards dressed in civilian clothes, the statement said.

"It is not clear at this time ... if these were a combination of civilian or Afghan security forces and civilians or something else," said ISAF spokesman Major Charles Anthony.

"One thing we know for sure is that they were Afghans, the Forward Operating Base was attacked by rockets from that location where the casualties took place, that much is very clear," he said.

The fact that the Taliban do not wear uniforms and operate from among the civilian population made identifying targets more difficult, Anthony said.

"There are probably eight to 10 incidents a day taking place all around this country," he said. "Sometimes it is very clear what has happened and occasionally it is not so clear."

A joint Afghan and ISAF investigation is under way to determine the status of those killed.

Elsewhere, U.S. led coalition forces and Afghan troops detained nine insurgents in the province of Ghazni, southwest of Kabul on Sunday, the U.S. military said in a statement.

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