In data published on Thursday, the firm detected the passage of the Hilda I, the Amber, the Silvia 1, and the Happiness I, which were carrying a total of seven million barrels of oil.

They all loaded their cargo in mid-April on Kharg Island, the country's main oil terminal, through which 90 percent of the Islamic Republic's crude oil normally transits.

The ships crossed the strait on Monday with their AIS transponders turned off.

Kpler relies primarily on satellite imagery to track ships transporting raw materials.

The four oil tankers typically transport Iranian crude to an offshore area off the coasts of Malaysia and Singapore, where they transfer the cargo at sea to other tankers (ship-to-ship) tasked with delivering it to the final customer, often in China.

Tehran adopted this practice to circumvent international sanctions.

The four tankers had initially continued their operations despite the conflict with Israel and the United States but had paused operations since April 13, when Washington imposed a blockade on Iranian ports in response to Tehran's blockade of the Strait of Hormuz.

Three other oil tankers linked to Iran had already defied the blockade on April 15, according to Kpler.

None had attempted to do so since then.

The US military regularly announces actions against oil tankers attempting to violate the blockade.

The US announced on Tuesday that it had disabled an oil tanker by firing on its engine room to prevent it from reaching Kharg Island.

This was the sixth vessel damaged by US military forces as part of the blockade.