NEW YORK ( TheStreet) -- The Securities and Exchange Commission is reportedly probing whether investment banks and private equity firms violated bribery laws in their dealings with sovereign wealth funds.

According to the Wall Street Journal, the regulatory agency has sent "letters of inquiry" to both Citigroup ( C) and Blackstone Group ( BX) among others. The article, which cited people familiar with the matter, said that as many as 10 such letters were sent in the past week.

The letters are reportedly requesting the firms supply documents related to their dealings with sovereign wealth funds, which are typically defined as investment vehicles run by foreign governments.

The Journal said one person familiar with the situation indicated the letters being sent were brief and didn't include specific allegations of bribery.

-- Written by Michael Baron in New York.

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