The government's position on food banks was mired in confusion after it emerged that David Cameron had enthusiastically backed their work at a Christian faith group's Easter reception, in contrast to biting criticism of the schemes made last week by Iain Duncan Smith's work and pensions department.

A row erupted on Wednesday after figures from the Trussell Trust, Britain's biggest food bank provider, revealed that almost a million people have sought three days' emergency food supplies over the last year.

The Christian charity also reported that government use of sanctions against benefit recipients was "increasingly harsh" and that half of those who had been referred to food banks in 2013-14 had suffered benefit delays or changes.

One senior DWP source accused the charity of "misleading and emotionally manipulative publicity-seeking", while another official said the rise in food bank use was down to the Trussell Trust "aggressively marketing their services".

But at a recent Downing Street event for Christian organisations, the prime minister praised the "provision of food banks". He said: "Whether it's providing services for children at risk of exclusion, whether it's teaching prisoners to read, whether it's dealing with breakdown, whether it's provision of food banks, there are some extraordinary organisations run by faith groups and Christians in our country and I want to see the possibilities for that to expand.

Chris Mould, chairman of the Trussell Trust, told the Observer Cameron also had a constructive half-hour meeting with the charity in February. Duncan Smith earlier refused to deal with the charity, accusing it of "scaremongering" and advancing a political agenda.

The contrasting responses reveal the government's struggle to react to growing food poverty even as economic recovery gathers pace. While the DWP chose to attack the trust as "publicity-seeking", Cameron emphasised the importance of charity and community engagement as part of his faith. Cameron wrote in an article for the Church Times that Christianity "compels us to get out there and make a difference to people's lives". His recent emphasis on religion is likely to appeal to Ukip voters, a poll revealed last week.

Christian leaders have increasingly put pressure on the government to tackle food poverty. On Wednesday, 36 Anglican bishops and more than 600 church leaders from all major denominations signed a letter demanding action from ministers. DWP officials last week briefed that Mould was "effectively running a business".

He responded, saying the attacks were "deeply disappointing and inconsistent with the message that we and many other charities took from the prime minister's Easter reception for the Christian faith". He said the criticism was more surprising given his fruitful meeting at No 10 earlier this year. "We had a frank and open conversation over 30 minutes. David Cameron had some very appropriate, probing questions to ask about the issues we're talking about. It was good dialogue."

Responding to accusations that his charity was "aggressively marketing", Mould said: "You can't get free food from the Trussell Trust by walking through the door and asking for it; you must have a voucher. More than 24,000 professionals – half of whom work in the public sector and health service, the police, and in social services – ask us to give this food to clients because they've made the decision that this individual or family is in dire straits and needs help. We're not drumming up demand."

The DWP last week claimed that food poverty has gone down under this government, pointing to a recent report by the Organisation for Economic Co-operation and Development. It found that the proportion of people in the UK who said they were finding it difficult to afford food had fallen from 9.8% in 2007 to 8.1% in 2012.

The Labour party has also waded into the row. Grahame Morris, Labour MP for Easington, said: "The huge increases in the reliance on food banks is directly related to the cost of living crisis and Cameron's cuts to welfare safety nets. The Trussell Trust only runs 37% of UK food banks so, if anything, their figures are a conservative underestimate of the number forced to rely on food aid."