The decisions are the most concrete examples so far of disruption to petroleum flows since Yemen’s Houthi militants stepped up attacks on merchant ships late last year.

For ships that heed the military advice, it means Egypt’s Suez Canal — a vital trade artery — is no longer a usable route to cut between Asia and Europe. It’s unclear how long the guidance will remain in place.

“Should the situation escalate, all ships must be expected to avoid the Red Sea until safe passage is restored and effectively close the Suez Canal for all ships” except for vessels that aren’t going all the way through the Red Sea, Niels Rasmussen, chief shipping analyst at trade group Bimco said.

READ: Shipping Advised to Avoid Key Trade Route After Yemen Bombed 

The leader of the Houthis vowed a big response to the attacks, underscoring the immediate need for caution among vessel owners.

Oil prices rose after the strikes. Brent futures were trading at $79.84 a barrel, a gain of 3.1%, at about 2:39 p.m. in London.

Less Impact

Torm, which has a fleet of about 80 tankers said it would stay away until further notice. Hafnia, which owns 117 carriers and operates about 90 more, and Stena Bulk, with about 60 also stated their decision to pause.

Until now, the majority of Houthi attacks on vessels have been against container ships carrying manufactured goods, causing a vast rerouting of trade for that part of the industry.

By contrast, the number of energy tankers diverted has so far remained relatively small.

Commodity trading giant Trafigura Group estimated on Thursday, before the strikes, that tanker movements through the area were down by 15% to 20%, echoing wider industry estimates.

At least eight tankers that were headed toward the Bab el-Mandeb Strait u-turned.

Even so, some vessels were still going through, digital vessel-tracking showed Friday. One shipbroker reported that most oil tanker owners have elected to pause transits through the area though some were continuing.

The ultimate impact on the oil market also depends on how much disruption there is to supply. The pausing of Red Sea transits mainly means deliveries taking longer — but it doesn’t necessarily mean fewer barrels.

Merchant shipping has a longstanding right to freedom of passage, meaning that vessels are still legally permitted to go through, although it’s not clear what the insurance status of such transits would be.

A long-term closure of the designated area in the Red Sea would likely increase demand for tanker, container, and dry bulk shipping by 12%, 11%, and 5% respectively, Bimco’s Rasmussen said.