UPDATE 1-Chocolate bar makers raided in German probe

(Adds comments from cartel office, chocolate makers)

FRANKFURT, Feb 11 (Reuters) - Investigators raided the German offices of chocolate bar makers Mars, Ritter, Nestle and Kraft, the companies said on Monday, on suspicion they colluded over price increases.

A spokeswoman at the Federal Cartel Office said its antitrust investigators searched seven chocolate makers on Thursday, on suspicion of price fixing in the German market early this year. She did not name the companies.

If the suspicion is confirmed, the companies could be fined up to 10 percent of their annual sales.

Nestle (NESN.VX: Quote, Profile, Research, Stock Buzz), Kraft Foods (KFT.N: Quote, Profile, Research, Stock Buzz) and Mars confirmed the raids at their offices and said they would cooperate fully with the authorities. Ritter also said its offices had been searched.

Investigators examined Nestle operations in Frankfurt on Thursday, a spokesman for Nestle in Germany said, confirming a report by the Financial Times Deutschland newspaper.

Silke Troesch, a spokeswoman for Kraft Foods Deutschland, said the investigators searched its offices in Bremen.

"We are cooperating fully with the authorities," Troesch said, adding that price increases were necessary due to recent sharp price rises in raw materials such as milk powder and cocoa.

A spokeswoman at Ritter said it raised its chocolate prices by about 20 percent in January.

(Reporting by Mantik Kusjanto, Tom Kaeckenhoff and Pascal Schmuck; Editing by Quentin Webb)