(AAP) - A dual Australian citizen held in Lebanon on terrorism-related charges has had his jaw broken while in detention, his cousin says.

Hussein Elomar was arrested early last month when the Lebanese army raided a workshop in Tripoli belonging to another Australian, Omar al-Hadba, and seized 500 kilograms of weapons.

It is alleged Mr al-Hadba supplied weapons to leaders of an al-Qaeda-led revolt near Tripoli.

A third dual Australian-Lebanese man, Ibrahim Sabouh, is also being charged, according to the Department of Foreign Affairs and Trade (DFAT), although the details remain unclear.

Two more Australians were initially arrested, including Mr Elomar's nephew, boxer Ahmed Elomar, but the charges were later dropped and both men were released.

Assam Elomar said in Sydney he was very concerned about his cousin Hussein, particularly as he claimed Ahmed was tortured in detention.

Mr Elomar said Ahmed had been forced to stand for long periods and was severely beaten if he tried to rest.

Ahmed's injuries included damage to his knee that seriously jeopardised his promising professional boxing career, he said.

"Of course I am worried about Hussein because I know he's getting, if anything, worse treatment than what Ahmed was getting," Mr Elomar said.

"He's still behind bars. What do you think they are doing? Giving him coffee and lunch and tea every day?

Australian diplomats had made repeated representations at the highest level over "serious allegations of mistreatment" of the three men, DFAT said today.

"The Australian Government must be able to do something about torture, we're not in the 1920s any more," he said.

DFAT says consular officials have visited the three men in detention and have offered assistance to their families in Lebanon.

"If they have visited him, why haven't they come back to the family? I haven't heard anything," he said.

He added his cousin's continued detention had been very stressful for his family in Sydney.

Hussein Elomar's wife and and uncle were in Lebanon but had found it difficult keeping informed about his well-being.

"It's not like you can just ring up and inquire about somebody. They just hang up the phone on you, they won't even answer any questions.

Mr Elomar said his cousin was innocent and suspected he had been arrested for knowing Mr al-Hadba.

"In Lebanon, if you have a friend who is involved in something but you didn't know about that, just you being his friend makes you guilty," he said.

"Look at Ahmed, the same thing happened to him. They torture first and work out, 'Oh, he's not involved, we'll let him go.' "