BEIRUT - Hezbollah chief Hassan Nasrallah acknowledged for the first time on Thursday that one of the Shiite group's militants was behind the downing of a Lebanese army helicopter last week.

Nasrallah said the downing was an accident that was understandable in the context of the high levels of alert maintained by the group's fighters in south Lebanon in the face of repeated Israeli attack over the years.

"The helicopter was flying over the hills and landed... Some of the brothers were surprised by the presence of a helicopter and one of them opened fire," Nasrallah said.

Last Friday, Hezbollah handed over the militant behind the shooting to Lebanese police, a judicial source said.

Nasrallah said the militant was an "honourable resistor" who had acted "naturally and instinctively" in opening fire and had asked to be turned in.

"Even in our training, mistakes happen," the Hezbollah leader said, adding that his group is "cooperating with the investigation to the very last phase."

Hezbollah has come under strong criticism within Lebanon over the shooting.

The group's continuing arsenal is a a major bone of contention between pro- and anti-Syrian groups within the confessionally divided country.