“On Thursday, Christian graves were desecrated for a second time in Benghazi,” Mohammed al-Quzairi of the local security committee told AFP, adding that the identity of the assailants was unclear.
The Benghazi civilian council said it was trying to track down those responsible.
“We are cooperating with the security committee to ascertain the identity of the assailants and bring them to justice as quickly as possible,” its spokesman, Khaled al-Jazawi, said.
A similar attack hit the same military cemetery in February.
The assailants shattered headstones of British and allied servicemen who fought in North African desert campaigns against the Nazis during World War II.
Reports at the time blamed the act on Salafists angered by the burning of the Koran at a NATO base in Afghanistan in early February.
Benghazi, Libya’s second city and the cradle of the 2011 revolt that toppled Muammar Qaddafi, has witnessed a wave of attacks against Western targets in recent weeks.
On June 6, the U.S. mission there was targeted by a small bomb which caused some material damage and wounded one person.
Less than a week later, on June 11, a convoy carrying the British ambassador to Libya was hit by a rocket-propelled grenade. The blast wounded two guards.
Earlier attacks targeted the International Committee of the Red Cross and a convoy carrying the top United Nations envoy to Libya, Ian Martin.
The violence comes as the country prepares to elect a general national congress, with the vote set for July 7.