(Adds details)

Nov 10 (Reuters) - Gilead Sciences Inc said on Thursday the U.S. Food and Drug Administration (FDA) approved its drug to treat chronic hepatitis B infection in patients with scarred liver.

The drug, Vemlidy, comes with a boxed warning, the strongest warning issued by the FDA that highlights serious risks such as lactic acid buildup, accumulation of fat on the liver or aggravation of the infection.

The drug has been approved as a once-daily treatment for the condition, which the World Health Organization estimates is responsible for more than 686,000 deaths every year worldwide.

Data from a late-stage study showed in January that the drug was not only effective, but also safer than the company's approved treatment, Viread.

Gilead's shares were down 0.7 pct at $77.90 in afternoon trading.

(Reporting by Dipika Jain in Bengaluru; Editing by Anil D'Silva)