Shares in Barclays fell as much as 6% in early trading on Tuesday, after one of its top investors offloaded a $1.2 billion chunk of stock in the lender at a discount overnight.

An unnamed investor sold 599 million shares on Monday evening, facilitated by Goldman Sachs. The shares are roughly equivalent to a 3.6% stake, according to Refinitiv Eikon data.

The sale deals a further blow to Barclays just a day after it disclosed a compliance blunder leading to an estimated 450 million pound ($589 million) loss for overselling structured products in the United States.

Barclays shares were last down 3.3% at 115.22 pence at 1004 GMT on Tuesday, after tumbling 4% on Monday.

Capital Group offloaded 399 million shares on Monday, according to Eikon data, but it was unclear whether the sale was connected to the transaction managed by Goldman Sachs.

Capital Group is one of the world's largest investment firms, and parent to the American Funds brand that is popular among millions of U.S. investors and retirement savers.

Capital Group declined to comment.

Other top Barclays shareholders with around a 3% stake in the lender include the Qatar Investment Authority (QIA) and Blackrock, according to Eikon data.

Blackrock declined to comment when approached by Reuters on Monday, while QIA was not immediately available for comment.

QIA last week offloaded 1.2% of miner and commodity trader Glencore for about $1.04 billion.

The Barclays sale was priced at 150 pence on Tuesday, towards the top of the target range of 147.50 pence to 150.75 pence, but this still represented a discount greater than 6% to Monday's closing price, pressuring the share price.

The sale was slightly bigger than the 575 million shares outlined on Monday evening, netting the seller 899 million pounds ($1.18 billion), a person involved in the deal told Reuters, adding the book was multiple times oversubscribed.

Barclays said on Monday it would have to delay a planned 1 billion pound share buyback because of the structured products loss, which it will have to incur as a result of buying back the securities in question at their original purchase price.

The regulatory blunder is an early test for C.S. Venkatakrishnan, the newly-appointed chief executive of Barclays, whose previous roles included heading the bank's global markets and risk operations.

($1 = 0.7640 pounds)