UPDATE 1-US FDA warns Philips health unit on plant problems

* Philips did not have proper complaint procedures - FDA

* FDA says company responses adequate, but must be checked

* Company says cooperating with FDA

WASHINGTON, Oct 20 (Reuters) - U.S. regulators warned the healthcare unit of Koninklijke Philips Electronics NV (PHG.AS) about manufacturing problems uncovered during an inspection of a plant in Massachusetts, a letter released on Tuesday said.

Food and Drug Administration inspectors found violations of federal manufacturing standards during a visit to a Philips Healthcare plant in Andover, Massachusetts, from January through March 2009, the letter said.

The FDA said the violations included the failure to maintain procedures to ensure all complaints about medical devices were processed in a uniform and timely manner.

The Oct. 9 letter, posted on the FDA website on Tuesday, said the company had adequately responded to the inspectors' findings, but "a follow up inspection will be required to assure that corrections are adequate."

Philips Healthcare spokesman Steve Kelly said the company "has been cooperative and responsive to all of FDA's requests, from the beginning of the inspection onward, providing detailed responses and offering documents to the FDA during and after the inspection."

Company executives also have offered to meet with the FDA to resolve any remaining questions, Kelly said. The follow-up inspection had not yet been scheduled, he said.

The FDA sends dozens of warning letters per year. Most issues raised in the letters are resolved without further action, although in rare cases they lead to product seizures or other actions. (Reporting by Lisa Richwine; editing by Andre Grenon)