UPDATE 2-US FDA: No letter to P&G on DayQuil, NyQuil

* FDA: Letter posted in error on Wednesday

* Agency says warning letter not sent to company (Adds company statement)

LOS ANGELES Oct 15 (Reuters) - A warning to Procter & Gamble (PG.N) about the marketing of some Vicks DayQuil and NyQuil products was posted in error and no letter has been sent to the company, U.S. regulators said on Thursday.

A U.S. Food and Drug Administration letter complaining about the company's labeling on DayQuil and NyQuil products with vitamin C was released on the agency's website on Wednesday.

The letter, dated Oct. 14, "was posted to the FDA website in error. The posting occurred due to an internal systems error, and no warning letter has been sent to Procter & Gamble," the FDA said in a statement issued on Thursday.

P&G spokeswoman Kate DiCarlo said the company "cannot speculate as to what might have happened, but we intend to work with the FDA to gain more information and resolve any concerns they might have."

In the letter, the FDA said P&G used false and misleading labeling on its Vicks DayQuil and NyQuil products with vitamin C.

The FDA's list of approved ingredients for over-the-counter cold-cough drugs does not allow for a combination of vitamin C with the other active ingredients in the two products, the agency said in the letter.

The letter also said the products were misbranded because vitamin C is included in the list of inactive ingredients.

The letter was withdrawn from the FDA website later on Wednesday.

In Thursday's statement, the FDA said it "regrets any confusion caused by the posting." (Reporting by Lisa Richwine and Ben Klayman; Editing by Steve Orlofsky, Bernard Orr)