The US Navy says Iran seized a commercial vessel that may have been engaged in smuggling as it sailed in international waters in the Arabian Gulf on Thursday.

It comes one day after Iran attempted to seize two oil tankers operating in the Gulf of Oman, but a US official stressed that the incidents are different, since the target of Thursday's seizure was likely a smuggling vessel.

A ship from Iran's Islamic Revolutionary Guard Corps Navy forcibly seized the chemical tanker Nada II, according to a US official. The US Navy monitored the situation, the official said, and after observing the crew's behavior and checking the history of the vessel, the Navy took no further action.

The seized ship made no distress call, the official said, and was likely engaged in smuggling.

The official said ships like this frequently smuggle sanctioned Iranian oil to sell it for a higher price abroad, but there is no way of knowing for sure what this particular ship was carrying.

"Ultimately, U.S. Naval Forces Central Command assessed the circumstances of this event did not warrant further response," said Commander Tim Hawkins, a spokesman for US Naval Forces Central Command. "U.S. forces remain vigilant and ready to protect navigational rights of lawful maritime traffic in the Middle East's critical waters."

One day earlier, the US Navy intervened to stop Iran from seizing two oil tankers in international waters in the Gulf of Oman. In the first incident early Wednesday morning, the US Navy observed an Iranian Navy vessel approaching an oil tanker.

The guided missile destroyer USS McFaul headed to the scene, at which point the US Navy says the Iranian vessel changed course and left the area.

But only hours later, a second Iranian Navy vessel approached another oil tanker in the Gulf of Oman, hailing the ship to stop in what the US Navy says was an attempted seizure. Iranian personnel opened fire with small arms towards the oil tanker, striking the ship near the crew living quarters, the US Navy said.

The oil tanker sent out a distress call, and the USS McFaul immediately headed to the incident at full speed. As the American destroyer approached, the Iranian Navy vessel changed course and left the scene.