A Pentagon assessment said it could take six months to completely clear the Strait of Hormuz of Iranian-laid mines, which could keep oil prices high, the Washington Post reported on Wednesday.

Iran has all but blocked the vital waterway since the start of a war with the United States and Israel, sharply driving up oil and gas prices and disrupting the global economy.

The strait—through which one-fifth of the world’s oil and gas passes in peacetime—has remained largely closed during a shaky ceasefire, with the US imposing its own blockade.