Shipping through the strategically important Strait of Hormuz fell sharply on Monday, when only one cargo vessel was recorded crossing the narrow waterway. The figure was the lowest daily level since May 7, according to preliminary data from shipping-monitoring firm Kpler. A large gas carrier entered the strait from the Gulf of Oman, while six vessels had moved through the route on Sunday.

Traffic has declined substantially in recent weeks amid worsening security conditions around the strait, one of the world’s most important energy transport routes. Vessel movements had already fallen into single digits on several occasions this month. Before the war began, nearly one-fifth of global crude oil and liquefied natural gas shipments passed through the Strait of Hormuz, raising concern over international energy supplies.

Kpler said its data remains preliminary because some ships travel with their transponders, or Automatic Identification System signals, switched off for security reasons. Actual traffic may therefore be higher than the published figure. Iran has also recently blacklisted 45 tankers and threatened them with fines, detention or cargo seizure, increasing risks for commercial shipping.