SHANGHAI (REUTERS) - China's foreign exchange regulator has ordered banks in some trading hubs to limit US dollar purchases this month, three people with direct knowledge said on Friday (Jan 8), in the latest attempt to stem capital outflows.

The spread between the onshore and offshore markets for the yuan, or renminbi, has been growing since the devaluation last year, spurring Beijing to adopt a range of measures to curb outflows of capital.

All banks in certain trading hubs, including Shenzhen, have been affected, the people added. They declined to be identified because they are not allowed to speak to the media.

Officials at State Administration of Foreign Exchange did not immediately respond to comment.

China suspended forex business for some foreign banks, including Deutsche, DBS and Standard Chartered at the end of last year.