The Air Force says it is tracking an “unmanned balloon without observable identification markings” after it was spotted over Kauai on Monday.

Dozens of Kauai residents reported seeing what several described as a strange circular object floating above the island for several hours, followed by the arrival of American military aircraft. Some witnesses said the object was glowing, and several claimed they saw the U.S. jets attacking the object and heard explosions.

The Air Force acknowledged the incident days later and said its pilots did not attack the balloon. But some Kauai residents, including a County Council member, still have questions.

“U.S. Indo-Pacific Command detected a high- altitude object floating in air in the vicinity of the Hawaiian Islands. In accordance with homeland defense procedures, Pacific Air Forces launched tactical aircraft to intercept and identify the object,” the Air Force said Wednesday in a statement.

“As part of our normal daily operations, we closely track all vessels and aircraft in the Indo-Pacific area of operations through a combination of joint capabilities to protect the U.S. homeland, support our allies and partners, and secure a free and open Indo-Pacific.”

Kauai Councilwoman Felicia Cowden didn’t witness the object Monday, but later saw photos and video that circulated on social media. She said she heard two loud booms and felt her house in Kilauea shake. Other Kauai residents also reported on social media that they heard booming sounds.

“I went outside to look to see if a tree or something fell on the roof. There were two significant booms maybe a minute apart,” Cowden said. “I would like to understand what were the powerful explosion sounds that were strong enough to shake my house in Kilauea, Kauai, and what looked like smoke in the sky,” she said. “Was any object hit and did it explode? If so, what was it and why?”

On Thursday, an Air Force spokesperson said pilots did not fire on the balloon.

“The responding aircraft did not destroy the balloon,” the spokesperson said in an email. “We are actively monitoring it via joint capabilities and it is under evaluation. We don’t have anything else to provide on this at this time.”

Balloons are commonly used for weather analysis and other scientific research. Some military and intelligence agencies also have used various balloons for surveillance and gathering intelligence. Many balloons are metallic, which can sometimes reflect sunlight in a way that makes make them appear as though they are glowing.

Kauai is home to the Navy’s Pacific Missile Range Facility, where it tests new missile technology and is now a proposed site for the $1.9 billion Homeland Defense Radar-Hawaii.