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China has complained to Zambia after 31 of its nationals were arrested at the weekend for alleged illegal mining practices.

A senior Chinese foreign ministry official is quoted as saying that the Zambian authorities have failed to provide strong evidence.

Those arrested are accused of, among other things, running unlicensed smelting plants and employing children.

China has invested heavily in Zambian copper mining and other sectors.

The country is also home to a growing Chinese community.

The arrests happened in a joint police and immigration operation in the town of Chingola, 400km (250 miles) north of the capital, Lusaka.

"We are here to put to an end this criminality. Foreign investors who come into this country must work within the confines of the law. Those who break the law will be flushed out," Home Affairs Minister Stephen Kampyongo was quoted as saying in the .

Lin Songtian, the Chinese Foreign Ministry's director-general for African affairs, said that while he supports measures to deal with illegal mining, in this case proof had not been provided, Reuters news agency reports.

He also complained that among those arrested was a pregnant woman and two others with malaria.

There has been some tension between the Chinese and Zambians in the past.

In 2010, two Chinese managers were accused of attempted murder after firing on miners during a pay dispute. The charges were later dropped.

Two years later, Zambian miners killed a Chinese manager during a riot at a coal mine.