TBILISI (Reuters) - Six Georgian soldiers were killed in southern Afghanistan on Thursday when a suicide bomber detonated a truck filled with explosives, the defense ministry said.

The attack takes the number of Georgian troop deaths in Afghanistan - where the former Soviet country has the largest non-NATO combat troop presence - to 28.

"It was a terrorist attack on our base ... Six of our soldiers died, nine were wounded," Irakly Dzneladze, the head of military staff, told a briefing.

He said the bomber drove the truck into the base in Helmand, the Afghan province where 1,500 Georgian troops are stationed.

It was the second such attack on Georgian troops in Afghanistan in a month. A suicide bomber killed three Georgian soldiers on May 13.

Georgian troops have been in Afghanistan since 2004, a commitment that underscores Tbilisi's ambition to join NATO, despite opposition from neighboring Russia, with which it fought a war in 2008.

"This is a tragedy for their families, for our country and each of us," Georgian President Mikheil Saakashvili said in a televised statement.

(Reporting by Margarita Antidze; Editing by Robin Pomeroy)