The White House is "dusting off old plans" for a potential release of oil reserves to dampen rising gasoline prices and prevent high energy costs from undermining the success of Iran sanctions, a source with knowledge of the situation said on Thursday.

U.S. officials will monitor market conditions over the coming weeks, watching whether gasoline prices fall after the Sept. 3 Labor Day holiday, as they historically do, the source said.

It was too early to say how big a drawdown would be from the U.S. Strategic Petroleum Reserve and, potentially, other international reserves if a decision to proceed was taken, the source said.

Oil prices have surged in recent weeks, with Brent crude prices closing in on $120 a barrel, up sharply from around $90 a barrel in July. The United States and other Group of Eight countries studied a potential oil release in the spring but shelved the plans when prices dropped.