Washington has pointed out that such actions represent a threat to maritime security.
The US special envoy for Iran, Brian Hook, said during a regular briefing that a dozen Iranian oil tankers turned off their automatic identification systems.
"On the basis of reliable data, we now know that up to a dozen Iranian oil tankers have recently shut down their marine transponders [automatic identification system] and, in fact, have disappeared from sight ," Hook said.
The official also pointed out that the deactivation of the so-called 'transponders' makes it difficult to determine the position of the ships, adding that such actions represent a threat to maritime safety.
In addition, Hook warned of the risks for countries that allow Iranian oil tankers to enter their waters .