The mother of an Australian activist detained in Israel says her son is being abused, including having his head slammed into concrete.

Surya McEwen was one of half a dozen Australians arrested by Israel when a humanitarian aid flotilla bound for Gaza was intercepted.

Hundreds of people, including Swedish activist Greta Thunberg, tried to sail to Gaza to deliver aid to civilians facing starvation and famine as Israel throttled supplies and the humanitarian crisis is at catastrophic levels.

Jacinta McEwen said she was distressed at her son’s treatment.

McEwen said her son was on a hunger strike and the water he was forced to drink was “undrinkable”.

“He’s being maltreated. He’s being intimidated. Threats have been made,” she told AAP.

“He’s had his arm dislocated and his head shoved into the concrete.

“I’m really begging our government to act now and bring him and other humanitarians, Australian citizens, home.”

McEwen said her son’s arrest was unlawful as it occurred in international waters.

Australian authorities made representations to Israel about the welfare and treatment of Australians on Sunday.

The Global Movement to Gaza has alleged McEwen has faced threats of sexual violence, physical assault, ongoing intimidation including verbal abuse and water that had an off taste while in an Israeli prison.

A spokesperson for the movement further cited reports of detainees being forced to kneel for more than five hours while having their hands zip-tied behind their backs, being denied food and water for extended periods and being subjected to sleep deprivation.

Israel’s foreign ministry has previously denied activists were being abused and said all prisoners’ legal rights were being upheld as reports about maltreatment surfaced from deported detainees.

The mother of Bianca Webb-Pullman, a Melbourne GP aboard the flotilla, said she was “worried sick” and frustrated with Prime Minister Anthony Albanese and Foreign Minister Penny Wong’s failure to condemn Israel’s actions.

A spokesperson for Senator Wong said Australia was providing consular assistance to seven Australians.

“We know this is a distressing time for them and for their loved ones. Our officials are doing everything they can to support them including through in-person visits,” the spokesperson said.

“We have made clear to Israel our expectation that detainees will receive humane treatment in line with international norms.”

Julie Webb-Pullman said 170 more flotilla members were expected to be released on Monday, but didn’t know if her daughter would be among the cohort.

“I won’t know until she’s out on the ground in whatever country they decide to send her to,” she told ABC Radio.

Webb-Pullman said her daughter was being held in Ketziot Prison but had only received reports of the conditions from detainees who had already been released.

“Some people have to sleep on the floor. They’re very overcrowded. The water is contaminated,” she said.

“But she has finally drunk the water because she … had had no food or water.”

-AAP