Six Russian oil tankers still under construction by Russia’s Zvezda shipyard were included in U.S. sanctions imposed last week, the first time Washington is known to have banned tankers before they even set sail, much less carried sanctioned cargo.

The sanctions imposed last week caused a spike in the price of oil and a surge in the cost of tanker shipping, as the outgoing Biden administration took steps to damage Russia’s oil exports and hinder attempts by Moscow to build its own fleet.

A Reuters review of the measures found that the six tankers under construction at Zvezda were among 183 vessels hit. They include the Nursultan Nazarbayev, the Alexander Beggrov, the Alexey Bogolyubov and three yet to be named: Zvezda 131080, Zvezda 131060 and Zvezda 131040.

Russia’s Sovcomflot is the buyer of the Alexander Beggrov and the Alexey Bogolyubov, according to the sanctions’ text, while Rosneft’s shipping arm Rosnefteflot is the buyer of the other four. Both buyers are also under U.S. sanctions.

Rosneft and the shipyard’s representative did not reply to Reuters requests for comment. The ministry of transport and Sovcomflot declined to comment. The U.S. Treasury Department’s Office of Foreign Assets Control did not immediately respond to a request for comment.

The sanctions target the so-called “shadow fleet” that Russia has used to avert a price cap imposed by the G7 countries in late 2022, which bans insurance and shipping from western providers for Russian oil sold for more than $60 per barrel.

Putting ships that are still being built under the sanctions could make it hard for Russia to justify the cost of completing them, an industry source involved in Russian oil trading said.

Russia is set to face a shortage of tankers for its oil exports after the sanctions, as more than 60% of the oil tankers listed have entered Russian ports during the last two months, Reuters research based on shipping data showed.

The shortage of ships for Russian oil has already led to a steep rise in freight rates worldwide.

Zvezda, established in 2015, is a leading Russian shipyard and the only one in the country able to build large-capacity oil and gas vessels. The shipyard itself was also subjected to last week’s U.S. sanctions.

Source: Reuters reported by Reuters in MOSCOW and Gleb Stolyarov in TBILISI, additional reporting by Timothy Gardner in WASHINGTON edited by Peter Graff