WASHINGTON, D.C. -- The destroyer USS Mason fired defensive countermeasures in response to what may have been incoming missiles, a defense official said . The ship had been attacked two times before in the past week, which triggered retaliatory strikes against radars used by Houthi rebels in those attacks. The Pentagon is investigating the incident.

"A U.S. Strike Group transiting international waters in the Red Sea detected possible inbound missile threats and deployed appropriate defensive measures," said a U.S. defense official. "Post event assessment is ongoing. All U.S. warships and vessels in the area are safe."

The destroyer USS Nitze and the USS Ponce, an afloat forward staging area ship, were close to the Mason at the time.

U.S. officials had said earlier Sunday that the Mason had come under attack from two inbound missiles that originated in Houthi-controlled territory in Yemen.

"We are aware of the reports and we are assessing the situation," a U.S. defense official had said earlier. "All of our ships and crews are safe and unharmed."

According to one U.S. official, an initial report indicated that the destroyer had deployed defensive missiles, which resulted in the interception of one of the missiles, and that the other may have fallen into the sea. It now appears the destroyer fired missiles at what may have been incoming missiles.

The "post-event assessment" will determine what actually occurred Saturday, the official said.

Another U.S. official said of Saturday's incident, "We will continue to defend freedom of navigation in this critical waterway, and we will take all necessary steps to respond to threats and defend our personnel and ships."

The latest incident comes just days after the United States military launched a retaliatory missile attack that destroyed three Houthi radar sites used in the previous attacks.

In the earlier attacks, three missiles fired at the USS Mason from Houthi-controlled territory in Yemen all fell into the sea. It remained unclear whether two of them fell on their own into the sea or because of the defensive countermeasures used by the destroyer's crew.

Those strikes led to U.S. retaliatory missile strikes on Thursday targeting radars were located in Houthi-controlled territory in Yemen. In a statement, the Pentagon warned that any new missile attacks risked another U.S. military response.

Friday, a senior Administration official said there was "no doubt" that Houthi militants were behind the missile attacks on the Mason. The official said it was unclear what may have motivated the attacks and speculated that there may be factions within the group who have different agendas.

The Houthis are an Iranian-backed rebel group that in January 2015 overthrew the Yemeni government. Since March 2015, they have been fighting a Saudi-led coalition that intervened militarily in Yemen to restore that government to power.