Oil prices eased a touch but held near one-month highs on Friday as they headed for a third weekly gain on a tightening global supply outlook after the U.S. imposed tariffs against countries buying oil from Venezuela and placed curbs on Iranian oil trade.

Oil prices edged lower on Friday, but were still on track to record a third straight weekly gain as US tariffs on buyers of Venezuelan crude and restrictions on Iran’s oil trade stoked supply concerns.

U.S. Secretary of State Marco Rubio vowed Thursday that the United States will respond forcefully if Venezuela attacks Guyana amid an ongoing territorial dispute that involves massive oil and gas reserves.

Secretary of State Marco Rubio was visiting Guyana amid ExxonMobil’s oil production there. Venezuela has asserted claims to a large region of the country. Mr. Rubio later flew to Suriname.

U.S. Secretary of State warned Venezuela on Thursday that it would be "a very bad day" for the South American country if it were to attack its neighbor Guyana or U.S.-based energy giant ExxonMobil , in comments that threatened unspecified action in such a case.