BEIJING -- Chinese police on Saturday brought back 37 Chinese nationals from the southwestern African country Angola, where they had been arrested for organized crimes against other Chinese citizens such as kidnapping, armed robberies, extortions and forcing women into prostitution.

Such crimes are a major concern for China, which has emerged as Africa's main trading partner and a major source of investment for infrastructure. As a result, a large number of Chinese are working and living on the African continent, but their presence has brought problems such as violent crimes among Chinese nationals, especially in politically volatile countries that provide fresh, fertile ground for Chinese criminals.

The Ministry of Public Security said Beijing sent a special police force to Angola, which worked with local police in the operation that destroyed 12 Chinese gangs, resolved 48 criminal cases and rescued 14 Chinese victims. At home, domestic police arrested another 24 suspects involved in the cases, the ministry said.

Following a request from Chinese authorities, the 37 suspects on Saturday were extradited to China, where they will face trial on charges including kidnapping, armed robbery and extortion. They arrived in Beijing on a charter plane, the ministry said.

Such crimes hurt Chinese businesses overseas and tarnish the country's image. The Chinese government also wants to be seen as being capable of protecting its citizens in foreign countries.

China Police, an online news site managed by the ministry, on Saturday ran three articles on crime fighting in Angola. In one article, Chinese detective Liu Feng said many poorly-educated, low-income Chinese became gangsters in Angola, and kidnapped Chinese businessmen in broad daylight for ransom.

To protect themselves, Chinese businessmen in Angola hired bodyguards, purchased bullet-proof vehicles, built homes that were difficult to access and disguised themselves when they went out, the article said.

The news site said there were 14 kidnapping cases in 2011 and five people died. Out of fear, many Chinese businesses closed down in the country's capital of Luanda and elsewhere. In addition to government projects, private Chinese businessmen are involved in trade, construction and food service in Angola.

Another article described the experience of two Chinese women lured to Angola with the promise of well-paying jobs in a Chinese restaurant there.

Once in Angola, they were forced into prostitution, the article said.