Following through on an old threat, Iran has effectively closed the Strait of Hormuz, cutting off a vital waterway that normally carries about a fifth of global oil and liquefied natural gas supplies, in retaliation for U.S.-Israeli strikes.

As oil markets worry about a global energy crisis, the United States has said it may consider escorting vessels through the strait, which could prove very hard to secure — something Yemen's Houthis proved in disrupting Red Sea shipping last year.

About a fifth of global oil and liquefied natural gas normally passes through the strait, where traffic has dropped by 97% since the U.S.-Israeli war against Iran began on Feb. 28, according to United Nations data. #OilPrice