By Adam Jourdan and Engen Tham

SHANGHAI (Reuters) - A Chinese regulator investigated Siemens AG last year over whether the German group's healthcare unit and its dealers bribed hospitals to buy expensive disposable products used in some of its medical devices, three people with knowledge of the probe told Reuters.

The investigation, which has not previously been reported, follows a wide-reaching probe into the pharmaceutical industry in China that last year saw GlaxoSmithKline Plc fined nearly $500 million for bribing officials to push its medicine sales.

China's State Administration for Industry and Commerce (SAIC) accused Siemens and its dealers of having violated competition law by donating medical devices in return for agreements to exclusively buy the chemical reagents needed to run the machines from Siemens, the people said.

Reuters was unable to determine whether Siemens had denied the accusations or if any action was taken against the company or the dealers.

A senior spokesman for Siemens in Germany said he was "not aware" of the investigation and declined to comment on specific questions about the investigation.

"We are not aware of any situation that conforms to what you describe," said Germany-based spokesman Matthias Kraemer in response to questions emailed to Siemens in China and to the group's headquarters. He declined to comment further.

SAIC declined to comment.

China-based lawyers said it was not uncommon for regulators to conduct investigations behind closed doors and for legal teams to then negotiate settlements to keep probes under wraps.

The Siemens investigation, which involved as many as 1,000 hospitals, could signal further probes into other medical device makers, one of the sources said. It comes as Beijing pushes hospitals to use more locally-made medical devices and reduce a reliance on imports that account for three-quarters of a Chinese market worth around $34 billion.

Other foreign medical device firms operating in China include General Electric, Koninklijke Philips, Medtronic and Johnson & Johnson.

"COMMERCIAL BRIBERY"

SAIC accused Siemens and its dealers of having committed "commercial bribery" under Article 8 of the Anti-Unfair Competition Law, the sources said, and the regulator took a tough line on a practice that, while technically illegal, is relatively common in China's healthcare sector.

Chinese medical institutions are prohibited from accepting donations under conditions that impede fair competition or otherwise affect procurement decisions, according to China's National Health and Family Planning Commission.