Six mysterious metal spheres that washed ashore last weekend at Forrest Beach in northern Queensland, Australia, are “suspected space debris,” the Australian Space Agency announced Monday on social media.

Informally dubbed “space balls,” the large objects are likely pressure vessels — heavy-duty containers of pressurized gases and liquids — from a rocket that reentered Earth’s atmosphere, according to the agency. The spheres were roughly twice the size of a basketball, local residents reported.

Although the space agency initially discouraged the public from going near the spheres, Queensland emergency responders have since removed the objects and determined them to be safe, the ASA confirmed. Agency officials say that further debris may be found.

“Never touch, move or recover suspected space debris and assume it to be hazardous until advised otherwise. Move away and contact emergency services,” wrote an ASA spokesperson in an email to CNN.

The agency is currently working with international authorities to determine which vehicle the space balls fell from, and which nation conducted a launch.