Image caption DEA agent Derek Maltz shows a poster with the names of common designer drugs

Anti-drug agents in the United States say 225 people have been arrested in a major international operation against synthetic drugs.

Some 1,100 lb (500kg) of drugs have been seized in the US, Drug Enforcement Administration (DEA) officials said.

Arrests have been made in the US, Australia, Canada, Barbados and Panama.

The drugs are sold largely to "teenagers and young adults" under names such as K2 and Vanilla Sky, said DEA chief of operations James Capra.

"The bottom line is that these drugs are being marketed to the most vulnerable part of our society," said Mr Capra.

'Bath salts'

Designer drugs are produced in clandestine laboratories and sold in colourful packaging, which the authorities say are aimed at appealing to younger consumers.

The operation was "a terrific result for law enforcement agencies across the globe," acting Australian ambassador to the US Graham Fletcher told the AFP news agency.

Project Synergy was launched in the US in December 2012, targeting the "upper echelon of dangerous designer drug trafficking organisations," says a DEA statement.

The drugs are often marketed as herbal incense or bath salts.

They are also sold as herbal blends, with chemicals that mimic the effects of cannabis and can be smoked.

"Designer synthetic drugs have caused significant organ damage as well as overdose deaths," says the DEA.

The millions of dollars in profits generated by the illegal production and sale of synthetic drugs are sponsoring terror groups in the Middle East, said Mr Capra.