Beirut  - A military investigation into last week's attack on a Lebanese army helicopter by the Islamic group Hezbollah was likely to expand the hypothesis that there was more than one person involved, judicial sources said Tuesday.

The sources said that based on testimony by co-pilot Mahmoud Abboud and other witnesses, military investigators have demanded that Hezbollah turn over three other men allegedly involved in last Thursday's helicopter shooting that killed military officer Samer Hanna in Sujed, southern Lebanon.

Hezbollah on Friday turned over one suspect to the judiciary saying he was the person who opened fire at the helicopter.

Meanwhile, sources close to Hezbollah said the group is reacting positively to investigators' demands, adding that a preliminary probe showed that there was no premeditated motive behind the attack.

It said the man who opened fire did so because he under stress as were the rest of his comrades who thought they were facing an Israeli military airdrop.

Security sources said the helicopter was hit by three bullets.

Last week, Hezbollah and Israeli officials were engaged in a war of words, threatening to attack each other.

Hezbollah chief Sheikh Hassan Nasrallah vowed last month to destroy Israel if it carried out threats to strike Lebanon.

He was referring to warnings by Israeli leaders that Lebanon's civilian infrastructure could become a target following the formation of a unity government in which the Hezbollah-led opposition has 11 ministries and the power of veto over cabinet decisions. (dpa)