Bullets used in a recent assassination attempt on the leader of Thailand's so-called Yellow Shirts have been found to have come from a military unit, the head of the Thai army has said.

Investigators found 84 bullet casings and an unexploded grenade where pro-government leader Sondhi Limthongkul was attacked in Bangkok, General Anupong Paojinda said on Thursday.

"Based on investigations, three of them were M16 [assault rifle] bullets which were distributed in the First Army region to the Ninth Infantry," Anupong said.
 
"As far as I know the bullets were distributed for drill practice. However, there are many units in this infantry and at this moment it is still under investigation how the bullets were leaked."

The army will prosecute anyone it finds who was involved in allowing the leak of the the bullets, Anupong said.

Anupong had previously denied speculation that military personnel may have been involved in the assassination attempt.

Serious injuries

Sondhi, who leads the People's Alliance for Democracy (PAD), was seriously hurt when up to seven men opened fire on his car in the Thai capital on Friday.

His driver and his aide were also badly hurt in the attack.

Following the attack, the PAD said that it believed "men in uniform" were to blame. The movement has in recent weeks appealed for reforms within the Thai army.

But Sondhi also has strong opposition from business rivals and the "Red Shirt" movement, which is loyal to Thaksin Shinawatra, who was ousted as prime minister in a 2006 coup following PAD protests.

The Red Shirts led a series of protests against the Thai government last week, prompting the government of Abhisit Vejjajiva to impose emergency law across Bangkok.