The U.S. Federal Reserve is investigating possible improper conduct in foreign exchange markets by large banking institutions, a spokesman said on Wednesday.

"The Federal Reserve is continuing to investigate in the foreign exchange markets in coordination with other authorities, including the Department of Justice,” the spokesman said in a statement.

The Fed also is working closely with authorities overseas, according to the statement.

The announcement was made as global regulators fined five major banks, including UBS, HSBC and Citigroup, $3.4 billion for failing to stop their traders from trying to manipulate the foreign exchange market.