Image caption One of the packages was opened at the Maryland Department of Transport headquarters

Two employees opening mail at two separate Maryland state government buildings had their fingers singed when they opened parcels that released smoke and odours, officials have said.

One package was opened at the Jeffrey Building in downtown Annapolis and another at the Maryland Department of Transportation building in Hanover.

Both packages were described as being roughly the size of books.

Initial reports suggested the packages had exploded at the state buildings.

"When both packages were opened there was a reaction that caused a flash of fire, a brief flash of fire, smoke and a smell," Maryland state police spokesman Greg Shipley said.

The first package was opened at the Jeffrey Building, which houses state offices and staff including the mailroom for packages sent to the Office of the Governor, at approximately 1230 local time (1730 GMT).

The second package was opened about 15 minutes later in Hanover, near Baltimore-Washington Thurgood Marshall International Airport.

One of the packages was addressed to Maryland Governor Martin O'Malley, according to reports, and the other to the state transportation department.

Mailrooms at state offices throughout Maryland were being quarantined until it could be determined if any other packages had been sent, Mr Shipley said.

Maryland State Police, Maryland Transportation Police and the FBI are investigating the incidents.

A US Homeland Security Department official said the department was monitoring the incidents.

Meanwhile, part of the main terminal at Dulles airport in Washington DC was closed off on Thursday as police investigated a suspicious package.

Flights were reported to be operating normally.