The Strait of Hormuz is too dangerous right now, even for the mighty U.S. Navy, which has been called upon to secure the narrow waterway and bring relief to the worst oil disruption ever.

Since the U.S.-Israel war on Iran started two weeks ago, traffic around the Persian Gulf choke point has come to a virtual standstill as the Islamic Revolutionary Guard Corps attacks commercial ships and tankers, keeping 20% of global oil supplies bottled up.

President Donald Trump and administration officials insist the Navy can escort ships, perhaps later this month as airstrikes continue to degrade Iran’s ability to launch missiles and drones.

But the U.S. military has reportedly turned down requests for protection so far. Defense officials told The Wall Street Journal Navy escorts aren’t currently feasible because Iran can still attack ships, adding they won’t happen until the threat of Iranian fire has eased.

Navy officials also told the Journal earlier this week U.S. warships and commercial vessels would face enormous risks, describing the Strait of Hormuz as an Iranian “kill box.” The Pentagon didn’t immediately respond to a request for comment.