Treasury said it has triggered a second round of stock sales through its agent, Morgan Stanley. That will involve an additional 1.5 billion shares.
The government said it would not sell shares during the blackout period set by Citigroup in advance of its second quarter earnings release.
That period is expected to begin on July 1. Treasury has previously said it hopes to sell all of its Citigroup shares this year.
The sales are the government's latest move to recoup the costs of the $700 billion financial bailout.
The stock sold for an average price per share of around $4.33, Treasury said.
The stock has traded in a range of $2.55 to $5.43 over the past 52 weeks.
The Financial Times reported Wednesday that the Qatar Investment Authority was considering buying a portion of Treasury's stake in Citi.
Treasury purchased the common stock in the summer of 2009 at a share price of $3.25. It received the original 7.7 billion shares of Citigroup common stock, which amounted to 27 percent of the company, in return for an investment of $25 billion in the company.
Citi, one of the hardest-hit banks during the financial crisis, received $45 billion in bailout money. That was one of the largest rescues by the government.
Of the $45 billion, $25 billion was converted to a government ownership stake in Citi last summer. The bank repaid the other $20 billion in December.