Israeli troops have been accused of stealing from activists arrested in the assault on the Gaza flotilla after confiscated debit cards belonging to activists were subsequently used.

One of the ships impounded by Israel when it raided the flotilla of aid vessels off Gaza. Photograph: Jim Hollander/EPA

Individual soldiers appear to have used confiscated debit cards to buy items such as iPod accessories, while mobile phones seized from activists have also been used for calls.

Ebrahim Musaji, 23, of Gloucester, has a bank statement showing his debit card was used in an Israeli vending machine for a purchase costing him 82p on 9 June.

It was then used on a Dutch website, www.thisipod.com, twice on 10 June: once for amounts equivalent to £42.42 and then for £37.83. And a Californian activist, Kathy Sheetz, has alleged that she has been charged more than $1,000 in transactions from vending machines in Israel since 6 June.

Musaji and Sheetz were on board two separate boats - one the Mavi Marmara, on which nine Turkish activists were killed, the other on the Challenger 1. Both activists only entered Israel when arrested, and were in custody for their entire time on Israeli soil.

"They've obviously taken my card and used it," Musaji told the Guardian.

"When they take things like people's videos and debit cards and use them, and their mobile phones, it becomes a bit of a joke.

"We were held hostage, we were attacked, and now there's been theft. If the police confiscate your goods in the UK, they're not going to use your goods and think they can get away with it."

Musaji cancelled his card on 7 June, the day after he returned to Britain, where he is a support worker for adults with learning difficulties. His bank has agreed to treat the transactions as fraudulent and he will not be charged for them. His mobile phone was also used for two short calls in Israel after it had been confiscated.

Another American activist, David Schermerhorn, 80, from Washington state, claims his iPhone was used, while Manolo Luppichini, an Italian journalist, said his card was debited with the equivalent of €54 after it was confiscated.

Activists say Israel still has possession of at least £1m of goods and cash, comprising aid and personal possessions, including laptops and cameras.

Some passports, three of them belonging to British citizens, have still not been returned. On Thursday, delegations in 12 countries, including the UK, held meetings with their respective governments to exert pressure on Israeli to return the seized property.

A spokeswoman for the Israeli embassy in London advised Musaji to register a formal complaint.

"We regard any misconduct as described in Mr Musaji's allegations to be utterly unacceptable and intolerable, and suggest waiting until this subject matter is clarified," she said. "As had happened previously, an Israeli soldier was found guilty of illegal use of a credit card for which he was indicted and sentenced to seven months' imprisonment."