Zimbabwe's government has banned at least one international aid group from operating in the country for allegedly campaigning for the opposition.
All operations of Care International are now suspended, pending an inquiry into the claims.
Care denies that it "has encouraged or tolerated any political activity".
The ban comes as Zimbabwe prepares for a run-off election between President Robert Mugabe and opposition leader Morgan Tsvangirai on 27 June.
Meanwhile, senior opposition figure Arthur Mutambara has been freed on bail, after being arrested on Sunday over a newspaper article.
After being released, he accused the government of a crackdown on opposition supporters ahead of the run-off - similar claims to those he made in his article.
There is a crucial run-off coming and our information indicates that NGOs are involved in plans to undermine our candidate
Nicholas Goche Social Welfare Minister
"What has happened is nothing compared to what the people of Zimbabwe are experiencing. Mugabe is violating the human rights of our people," Mr Mutambara said.
In another case, three South Africans have been jailed for six months for working as journalists without accreditation, reports the state-owned Chronicle newspaper.
They were arrested last week, allegedly in possession of broadcasting equipment bearing the logo of the UK-based Sky News.
"This country is not a banana republic. It has laws which must be observed and respected by both its citizens and foreigners," magistrate John Masimba was quoted as saying.
The government has introduced strict media laws in recent years but several journalists have been reporting undercover on the elections.
Addressing the UN food summit in Rome, Mr Mugabe said the West, led by the former colonial power in Zimbabwe, Britain, was plotting to effect "illegal regime change" against him.
"Funds are being channelled through non-governmental organisations to opposition political parties, which are a creation of the West," he said.
MDC faction leader Arthur Mutambara criticises Mugabe outside court
He defended Zimbabwe's land reforms, saying he had "democratised" land ownership in the country, turning 300,000 previously landless families into land-owners.
The land was seized from some 4,000 white farmers, which critics say has destroyed Zimbabwe's once thriving economy.
The UK and Australia say Mr Mugabe's presence at the food summit is "obscene", saying his policies have caused starvation.
Some four million Zimbabweans - a third of the population - are believed to need food aid.
Earlier, Zimbabwe's Social Welfare Minister Nicholas Goche was quoted as saying that several aid agencies could have their activities halted.
"Several other non-governmental organizations involved in food distribution in Manicaland province will also be asked to cease operations while we investigate them," he told the ZimOnline website.
"There is a crucial run-off coming and our information indicates that NGOs are involved in plans to undermine our candidate."
An official from another aid agency told the BBC News website that his group had been ordered to cease work in parts of Manicaland.
He said the agency had scaled back its operations during the elections after similar comments from ministers in the past.
Care says it has strict rules against getting involved in politics.
"Care has requested but has not yet received any details of the allegations, including names, dates and locations," the agency said.
Care says some 500,000 Zimbabweans were affected by the suspension.
"Care has pledged to co-operate with the [Zimbabwean] government in resolving the situation, so the humanitarian operations may resume as soon as possible."
Kenneth Walker, Care's Africa communications manager, told the BBC News website that the group's operations were suspended last Friday.
Mr Walker said Care had been accused of being involved in the distribution of brochures on behalf of Mr Tsvangirai's Movement for Democratic Change (MDC) and threatening to withhold food from those not supporting the opposition.
Care is involved in a number of projects in Zimbabwe, including distributing food aid, water and sanitation, micro credits and support for orphans.
The MDC has frequently accused the government of denying food aid to opposition supporters - accusations denied by the authorities.
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