Justice Department investigators believed that Google Inc's Chief Executive Larry Page knew about improper online pharmacy ads that Google carried, and allowed the ads for years, the Wall Street Journal said.

On Wednesday, Google agreed to pay $500 million to settle a criminal probe into ads it accepted for online Canadian pharmacies selling drugs in the United States.

Larry Page knew what was going on, Peter Neronha, the Rhode Island U.S. Attorney who led the probe, told the Journal.

Neronha was not immediately available for comment.

Prosecutors found internal emails and documents that, they say, show Page was aware of the allegedly illicit ad sales, the newspaper said.

The Justice Department said earlier this week that the advertisements led to illegal imports of prescription drugs into the country.

The Justice Department contends that Google knew it was potentially violating U.S. law since at least 2003, but didn't take effective action to ban the ads until it mounted an undercover sting operation against the Internet search giant in 2009, the journal said.

As we've said, we take responsibility for our actions. With hindsight, we shouldn't have allowed these ads on Google in the first place, a spokesperson for Google said in an email.

(Reporting by Anand Basu in Bangalore; editing by Carol Bishopric)

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