Washington (CNN) A U.S.-flagged ship was recently intercepted by an Iran Revolutionary Guard naval patrol, the U.S. Navy revealed to CNN Tuesday.

The incident occurred on Friday when four Iranian naval vessels surrounded the U.S.-flagged Maersk Kensington in the Strait of Hormuz.

The episode came ahead of an encounter Tuesday in which Iran Revolutionary Guard patrol boats fired shots at a commercial cargo ship and then intercepted the vessel, the Marshall Islands-flagged M/V Maersk Tigris, which was also crossing the Strait of Hormuz.

A senior U.S. military official told CNN that "the Iranians encircled the Kensington and followed the ship on its course for a period of time before withdrawing and breaking away." After that, the U.S. Navy Fifth Fleet issued a notice to mariners about the incident.

The crew of the Maersk Tigris container ship is "safe and under the circumstances in good spirits," Danish shipping company Maersk said Wednesday in an emailed statement to CNN. The Pentagon estimates that about 30 individuals are on board.

On Tuesday night, the cargo ship was being escorted toward Bandar Abbas on the coast of Iran by Iranian patrol boats, but it has not reached the shore. It's currently about 9 miles due south of the port.

Maersk said they are still unable to "establish or confirm the reason" for the seizure, and remain in close dialogue with the Danish Foreign Ministry.

Referring to Tuesday's incident, Pentagon spokesman Col. Steve Warren said it was "inappropriate" for the Iranians to fire the warning shots.

The U.S. Navy has dispatched one maritime patrol and reconnaissance aircraft to observe and monitor the situation, Warren told reporters.

Despite reports in some media, there are no Americans on board, according to a U.S. official.

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At this point, no U.S. military action is expected on the ship that was seized Tuesday aside from monitoring the situation. The U.S. believes that Iranians will "send the ship on its way," the senior official said.

State Department spokesman Jeff Rathke noted Tuesday afternoon that he U.S. has a security compact with the Marshall Islands on defense issues.

But he added that there hasn't been a specific request for assistance from the Marshall Islands and said it was premature to say whether this could require the use of force.

He did state, however, that "it's a key concern of the United States to ensure that sea lanes in the region remain open and safe."

In Tuesday's incident, the Marshall Islands-flagged vessel was transiting the Strait into the Persian Gulf on an internationally recognized maritime route when the Iranian military contacted the vessel and directed the ship master to "divert further into Iranian waters," according to Warren.

"The master was contacted and directed to proceed further into Iranian territorial waters. He declined and one of the IRGCN craft fired shots across the bridge of the Maersk Tigris," said Warren, referring to the Iranian Revolutionary Guard Corps Navy. "The master complied with the Iranian demand and proceeded into Iranian waters in the vicinity of Larak Island."

After the shots were fired, the Tigris issued a distress call that was picked up by U.S. forces in the area, and the USS Farragut was ordered to head towards the incident. The closest U.S. warship was 60 miles away.

"We have been in communication with U.S. shipping industry representatives with regards to how their vessels should respond to threatening encounters with foreign naval forces and how to contact us, " the U.S. official said, declining to provide the specific advice being given. In the incident Friday, no shots were fired.

The senior official pointed out that that historically, Iran Revolutionary Guard naval forces have been more likely to be engaged in hostile contact with the shipping and military vessels in the region than the regular Iranian navy. Contact with regular Iranian naval forces is frequent and "professional," the official said.

Even though the Strait of Hormuz is in Iranian territorial waters, "innocent passage" is applied -- ships are authorized to pass through the body of water assuming they abide by all the rules of the sea -- because it is an internationally recognized shipping lane.

Warren said it was "to be determined" what the USS Farragut will do when it reached the vicinity of the incident.

The M/V Maersk Tigris was seized at the request of Iran's Ports and Maritime Organization, Iran's semi-official news agency FARS is reporting, citing informed sources. The Marshall Islands-flagged vessel was seized after a relevant court order was issued, according to the source, indicating that the IPMO had monetary differences with the ship owner.

Maersk LInes issued a statement Tuesday that the company's "paramount concern is the safety and well-being of the crew."