A number of schools in the US were closed down on Wednesday after posted on a social networking site.

The threat, which apparently came from Australia, led to the lockdown of all schools in the mid-western US city of Minneapolis.

Police say they were alerted to the on-line threat, in which a young man threatened to "shoot up" an unspecified school in Minneapolis before killing himself.

It is believed an American teenage boy who now lives in Australia could have made the threats which affected about 34,000 students at 60 schools.

The schools were put into a lockdown mode, which meant children were confined to their classrooms.

The measure was lifted at the end of the school day.

Officials in the US and Australia are now trying to determine who was responsible for the Internet posting.