Cargo tracking group Vortexa told ABC News it identified 34 sanctioned or Iranian-linked ships moving in and out of the Gulf of Oman through the U.S. blockade of Iranian ports which came into effect on April 13.
Fifteen of those were inbound toward Iran, while 19 were outbound away from Iran.
Of the observed outbound movements, six of the ships were confirmed to be laden with approximately 10.7 million barrels of Iranian crude oil.
However, after Vortexa shared its data and media outlets named three of those ships, U.S. Central Command (CENTCOM) publicly refuted that the three named ships had evaded the blockade.
CENTCOM said two of those ships -- the Hero II and Hedy -- had returned to an Iranian port, and that the third -- the Dorena -- was "under the escort of a U.S. Navy destroyer in the Indian Ocean after previously attempting to violate the blockade."
It was not immediately clear whether the M/T Majestic X, which the U.S. announced Thursday it had interdicted in the Indian Ocean for carrying oil from Iran, was also one of the ships tracked as having moved through the blockade.
Vortexa said that the blockade is having some effect but, "based on observed vessel activity, flows have continued, although in a more constrained and selective environment."
TankerTrackers.com, a maritime intelligence company that tracks crude oil shipments, told ABC News that they observed nine shipments of Iranian oil pass through the U.S. blockade between April 13 and 20, one of which has been sent back to Iran.
Of the nine shipments, eight were tankers belonging to Iran's National Iranian Tanker Company and one was independently-owned.
-ABC News' Victoria Beaule and Chris Looft
