Gold had the biggest drop in almost two weeks after the Federal Reserve said it would extend its Operation Twist program, while refraining from announcing additional debt purchases.

The central bank will expand its program to replace short- term bonds with longer-term debt by $267 billion through the end of the year in a bid to reduce unemployment and protect expansion, policy makers said Wednesday in a statement. The Fed bought $2.3 trillion in assets through June 2011 in two rounds known as quantitative easing.

“The market is disappointed, and we are seeing some sell off,” Bart Melek, the Toronto-based head of commodity strategy at TD Securities Inc., said in a telephone interview. “The market had begun unwinding in the past few sessions since expectations were mixed, so I think the sell off will not be a very huge one.”

Gold futures for August delivery fell 0.5 percent to settle at $1,615.80 an ounce at 2:04 p.m. on the Comex in New York, the biggest drop for a most-active contract since June 7.

Silver futures for July delivery rose 0.1 percent to $28.389 on ounce.

On the New York Mercantile Exchange, platinum futures for July delivery fell 0.9 percent to $1,466.80 an ounce. Palladium futures for September delivery slipped 1.6 percent to $619.50 an ounce.