Some employees at GlaxoSmithKline who are being investigated in China for suspected bribery and tax-related violations have already confessed to the offences, according to the state-owned Xinhua news agency.

The latter was reporting on a statement issued by China's Ministry of Public Security which is looking into "serious economic crimes", and has directed police in Shanghai and the provinces of Hunan and Henan to investigate further. The suspects are believed to have offered large bribes to government officials, medical industry associations and foundations, hospitals and doctors.

The MPS says that the bribes were generally paid through travel agencies or as "project sponsorships". GSK is also suspected of being involved in tax-related crime, according to the ministry which says that the offences have been occurring "for some time, involving a large number of people and significant amounts of money".

The MPS statement comes days after GSK said it was investigating fresh allegations that staff in China were involved in paying backhanders to doctors to sell Botox (onabotulinumtoxin A), Allergan's drug which GSK sells in the country for therapeutic indications.

The Wall Street Journal had previously reported that an anonymous whistle-blower presented GSK in January with allegations that between 2004 and 2010 its staff provided doctors with speaking fees, cash payments, dinners and all-expenses-paid trips in return for prescribing its products. The allegations led to an internal probe, which GSK has previously said turned up no evidence of corruption or bribery.

A GSK spokesman told the WSJ that the Botox-related allegations may have come from the same source who has made previous claims of alleged corruption and bribery. He added that "our inquiries to date have found no evidence of bribery or corruption in relation to our sales and marketing of therapeutic Botox in China".