JOHANNESBURG, June 13 (Reuters) - Zimbabwe's ban on international aid organisations has left hundreds of thousands of children in the country without healthcare and food, the United Nations Children's Fund said on Friday.

President Robert Mugabe's government last week ordered all international aid groups and NGOs to stop their field work in a clampdown ahead of a June 27 presidential run-off election.

"The net effect is as many as 500,000 children are now not receiving the health care, HIV/AIDS support, education assistance and food that they require. Many of these children are orphans," UNICEF said in a statement.

UNICEF's regional director for East and Southern Africa said many children in Zimbabwe would not be able to endure going through the southern hemisphere winter without support.

"The level of suffering for these children increases daily," Per Engebak said. The aid group said political violence since a disputed March 29 first-round election has led to thousands of children not returning to school and several have become victims of the violence, some as young as two.

"This appalling violence damages children, their potential, and Zimbabwe as a whole. It must stop and it must stop now. All authorities have a legal obligation to protect children," Engebak said.

Zimbabwe's opposition Movement for Democratic Change (MDC) said the ruling ZANU-PF party has orchestrated a brutal campaign to cripple the opposition which has killed 66 of its supporters since elections in March. Mugabe blames the violence on the MDC.

Mugabe and ZANU-PF were defeated in March for the first time since independence in 1980 but Tsvangirai failed to win the presidential vote outright, necessitating a second round. (Reporting by Marius Bosch, editing by Mark Trevelyan)

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