Seven US Marines have been killed and eight more injured after a mortar shell exploded unexpectedly during a training exercise in the US state of Nevada.

Those caught in the blast at the Hawthorne Army Depot at 22:00 local time (05:00 GMT on Tuesday) were members of the 2nd Marine Division.

It was not immediately clear whether the 60mm mortar shell exploded prematurely inside its firing tube or whether more than a single round exploded

At least eight men are in hospital, three in a serious condition and five in a stable condition.

Investigation under way

The victims were airlifted to Renown Regional Medical Center in Reno with injuries that included penetrating trauma, fractures and vascular injuries, said Stacy Kendall, a spokeswoman for the facility.

Army and Marine officials said the incident is now under investigation.

Hawthorne Army Depot is a military facility used for the storage and destruction of demilitarised ammunition. It is located about 152km southeast of Reno.

The depot was first established as a naval staging area during most of World War II.

The names of the dead and injured have not been released pending notification of their families.

The accident comes a week after a US military plane assigned to a Washington state Naval Air Station crashed during
a routine training flight, killing all three crew members on board.

Source: Agencies