Authorities in Guam have arrested seven Chinese citizens accused of illegally entering the island during a key U.S. missile defense test. Guam’s Customs and Quarantine Agency confirmed the arrests, stating that four of the individuals were found near a military installation.

The arrests occurred between Dec. 10 and 11, around the same time the U.S. Missile Defense Agency conducted a missile interception test at Andersen Air Force Base. The test utilized advanced radar technology, which is part of a broader effort to strengthen Guam’s missile defense capabilities.

Officials say all seven individuals traveled by boat from Saipan. Investigators are working to determine the reasons behind their presence on the island. The Institute for the Study of War raised concerns that such incidents could be linked to espionage efforts, as Chinese intelligence operations often target military installations.

Guam is a strategic location for the U.S. military, hosting several bases and defense projects. Plans are underway to establish an air and missile defense network with cutting-edge systems, a project estimated to cost $10 billion over the next decade.

The successful missile interception test on Dec. 10 is part of ongoing evaluations by the Missile Defense Agency. Officials have stated that up to two tests may occur annually to enhance readiness and deterrence.

China’s Ministry of Foreign Affairs has not commented on the incident or the arrests.