WikiLeaks, the website that has published thousands of confidential US embassy cables, has donated $15,100 (£9,500) to the legal defence fund of Bradley Manning, the soldier accused of handing providing it with the digital trove.

WikiLeaks had been coming under mounting criticism from Manning's supporters to honour a pledge made last July to take on board a substantial part of the financial burden of the soldier's defence. The fund is managed by Manning's Rhode Island-based lawyer, David Coombs.

Manning has been charged with the disclosure of unauthorised material and is expected to face an article 32 hearing – the preliminary military procedure ahead of a court martial – in March. He was arrested last May in Iraq, where he was stationed on intelligence duties, and has been kept in solitary confinement for the last five months in a military jail at the Quantico marine base, Virginia.

WikiLeaks' slow response in coming to the financial aid of its alleged source, who now faces up to 52 years in prison for having passed information to the website, has long been a cause of frustration for his supporters, although they have been hesitant to go public.

In the past the Bradley Manning Support Network has indicated that WikiLeaks had promised to pay up to $50,000 in legal fees, although that offer was reduced to $20,000 in December and the payment ended up being $15,000.

Part of the problem may be explained by WikiLeaks' own financial difficulties as a result of Visa, MasterCard and PayPal cutting off its accounts after pressure from the US government.

The support network calculates that the legal fund needs to have at least $115,000 to fight a vigorous defence. Including the WikiLeaks donation, it has collected more than $100,000.

Jeff Paterson, a member of the support network's steering committee, said the financial target had almost been met so the focus of the campaign would switch from fundraising to publicising what the treatment of Manning, which he said was inhumane.

"Internationally, people are speaking out against the unjust imprisonment of Bradley Manning, who is accused of acting out of moral conviction," Paterson said.

Manning is being held in solitary confinement under a prevention of injury order despite having been cleared by a military psychologist earlier this year.

David House, a Massachusetts Institute of Technology researcher who is allowed to visit Manning, has reported a steady deterioration in his condition. Last month the UN office on torture announced it was launching an investigation into the soldier's treatment at Quantico.