US and Australian agencies have worked together on the largest-ever bust of a global synthetic drugs ring, seizing thousands of kilograms of illicit drugs and arresting 225 people in five countries.

US officials say millions of dollars in profits from the trafficking are being funnelled to groups in the Middle East, strongly hinting that terror networks are involved.

WASHINGTON: James Capra, chief of operations for the US Drug Enforcement Agency, speaks at a news conference at DEA headquarters. Brendan Hoffman/Getty Images/AFP. Credit:Brendan Hoffman

Authorities seized up to 1500 kilograms of "dangerous designer synthetic drugs" that were manufactured in Asia, notably China and India, and trafficked to the US and Australia, where dealers sold them to youths and young adults, the US Drug Enforcement Administration said.

US officials highlighted the international nature of the operation, particularly the involvement of agents in Australia, where the drugs have been marketed.