Federal security workers have started using hand-held scanners to inspect bottled carry-on liquids for explosives at some of the United States' busiest airports, the US government said on May 22.

The US Transportation Security Administration (TSA) has finished testing the device at Miami International Airport and Newark Liberty International Airport. Testing is ongoing in Los Angeles, Detroit and Las Vegas, said agency spokesman Nico Melendez. Testing will begin in Boston, the Associated Press reported.

TSA expects to deploy about 200 of the devices at a number of airports around the country by October, Melendez said.

The technology, which detects explosive material in sealed bottles of liquid, is only used on passengers selected for secondary inspections before boarding.

The device adds another layer of security to government restrictions on carry-on liquids instituted in September 2006 following revelations in August 2006 about an alleged terrorist plot.

Authorities say Britain-based terrorists were planning to construct bombs onboard aircraft from small amounts of liquids or gels carried in innocent-looking containers.

The scanning device, made by Washington-based ICx Technologies, has been previously employed by the US government for other uses.