Mr Ahmed's supporters want his immediate release

Shahana Ahmed alleged that the pair face political harassment for their work, which includes women's' projects.

She said that the authorities had not proved corruption allegations against them, and they should be freed now.

The Bangladeshi authorities have so far declined to comment on the detention of the two men.

Amnesty International have backed the call, saying the detainees face torture by police wanting to extract confessions.

Poverty alleviation

Qazi Faruque Ahmed and his colleague David William Biswas were arrested on Saturday in what police say are charges relating to financial irregularities within their Proshika organisation.

Proshika is one of the largest non-governmental organisations (NGOs) in the world, employing thousands of people in poverty alleviation, education and development projects.

Mr Ahmed is president of Proshika, and Mr Biswas is his deputy.

Proshika says it is working to help women

Speaking to the BBC from the prison where is detained, Mr Ahmed said that he did not know why he had been arrested.

Police said it was because of allegations filed by the Bureau of Anti-Corruption, which include financial irregularities within Proshika. Similar reasons were cited by police for the arrest of Mr Biswas.

The arrest of the two men has been strongly criticised by their families and the human rights group, Amnesty International.

Mr Ahmed's wife, Shahana, said that the allegations against the pair had been dismissed by international donors as baseless.

She urged the government to withdraw what she says are false cases against them.

And in a letter to the Bangladeshi prime minister, Amnesty International complained that the pair were being denied permission to speak to anyone and were "at grave risk" of torture in order to extract confessions.

Proshika has been the target of what appears to be politically motivated harassment for its alleged involvement in political activity Amnesty International report

Amnesty pointed out that Proshika was one of the country's leading NGO and its officials have been the target of government persecution since the general elections in 2001.

It said the authorities had blocked donor funds to Proshika and placed it under investigation for alleged financial irregularities.

Ministers in April accused Proshika of taking an anti-government political line during an opposition campaign to unseat the Prime Minister, Khaleda Zia.

Although it denied the allegations, the NGO's headquarters were raided and its cultural office was sealed off.

The BBC's Waliur Rahman in Dhaka says that the latest twist to the story has been provided by some Proshika officials who revolted against Mr Ahmed and demanded his removal.