A car exploded in Barsis, 50 km (30 miles) east of the port city, an army official told Reuters. "A car approached with great speed and then exploded. It appears to be a suicide attack," he said.
Three soldiers and three civilians were wounded and the alleged attacker was killed, the officials said, after first putting the death toll at two.
"There are body parts spread all over ...so we first thought two people had been killed," one army official said.
A suicide bomber hit the same army checkpoint in December, killing 13 soldiers, in the first suicide attack since the 2011 ouster of Muammar Gaddafi.
Some soldiers of the targeted army unit had declared support for a military campaign launched by retired army general Khalifa Haftar against Islamist militants months ago. More than 100 people have been killed in fighting, mainly in Benghazi, since then.
Haftar has accused the weak central government in Tripoli of failing to tackle Islamist militants such as the Ansar al-Sharia group, which has its own checkpoint in Benghazi.
Libya has been embroiled in strife as the government and parliament are unable to control militias, militants and armed tribesmen who helped topple Gaddafi but now defy state authority. REUTERS