The first American soldiers to die in American-Israeli war with Iran were killed in an alleged Iranian drone attack on a makeshift office space in Kuwait, three U.S. military officials with direct knowledge of the Iranian attack told CBS News.

There were at least six Americans killed in an attack on a tactical operations center in the port of Shuaiba in Kuwait, one of several U.S. allies in the Persian Gulf region that have faced intense Iranian missile and drone attacks since the U.S. and Israel launched strikes on Iran early Saturday. US Central Command publicly confirmed the death.

Defense Secretary Pete Hegseth said the deadly strike was caused by powerful Iranian weapons that went through air defenses and through the operations center’s fortifications.

“You have an air defense and there’s a lot coming in and you’re hitting most of it,” Hegseth said during a Pentagon news conference. “Every once in a while, you might have one, unfortunately, we call it a squirter, that breaks through. And in that particular case, it happened to hit a tactical operations center that was fortified, but these are powerful weapons.”

But three US military officials questioned the claim that the building was adequately fortified. They told CBS News that the operations center is a triple-wide trailer converted into office space – a common practice at US bases overseas.

The trailer’s only fortifications were the T-walls, which are 12-foot-tall, steel-reinforced concrete barriers used to protect military personnel from explosions, rocket attacks and shrapnel, military officials said.

But the T-walls could not protect the object from an overhead impact. Two officials told CBS News that the impact appeared to hit dead center at the top of the building.

The three officials also told CBS News, speaking on condition of anonymity because they were not authorized to speak to the media, that before the attack there were discussions on the ground about whether the tactical operations center in question should be used because it concentrated too many American troops in an indefensible location.

Preliminary battle damage assessments indicate that the operations center in Kuwait was attacked by a one-way drone, according to three U.S. military officials with direct knowledge of the Iranian attack. It is not clear which type it is, but Iran usually uses Shahed-136 “kamikaze” drones.

Fire engulfed the buildings, making it difficult to retrieve bodies immediately after impact, officials told CBS News.

Two of the three sources told CBS News they did not recall hearing the warning sirens typically associated with counter-battery systems designed to detect incoming enemy weapons that ultimately killed the service members. They also said the warning siren had been on for a week before the attack on the tactical operations center, but in previous incidents some of the drones were already at the base before the siren went off.

In addition, the two sources said there were no US anti-missile, artillery and mortar systems at Shuaiba port that could be used to shoot down incoming drones or other lethal munitions. Kuwait had interceptors nearby, but it is not clear if they were used.

Requests were made for more capabilities to defeat incoming drones, but those additional resources never arrived, two of the sources said. One source told CBS News, “We basically had no ability to defeat drones.”

“I’m sorry for their families’ losses,” one source told CBS News. “They were good people who did what their nation asked them to do.”

CNN first reported about the six soldiers killed in the port of Shuaiba and that they apparently had no prior warning. CBS News was the first to report the type of ordnance that hit the operations center, and that some US troops believe the center’s defenses were inadequate and that the operations center in place may not have been used in the first place.

Asked for comment, the Pentagon referred CBS News to US Central Command previous statements about fallen soldiers.

In addition to the six killed in Kuwait, at least 18 members of the military have been seriously wounded since Monday morning in a combat operation dubbed Operation Epic Rage, a spokesman for US Central Command told CBS News.

Hegseth called the military members who were killed “the absolute best in America.”

“Can we process the rest of this operation in a way that honors them,” he said.