At least five people were shot dead early Monday by a suspected gunman outside the northeastern U.S. city of Philadelphia, local media reported.

At least five people were shot dead early Monday by a suspected gunman outside the northeastern U.S. city of Philadelphia, local media reported.

The shootings, which ABC television affiliate WPVI said were thought to have been committed by a male military veteran, were said to have taken place at three different locations in suburban Philadelphia.

SWAT teams were called to a possible fourth scene in Pennsburg, it added.

Police told WPVI that the suspect was barricaded inside a home in Souderton, one of the sites where bodies were found, along with Lansdale and Lower Salford Township. SWAT teams were taking position outside the home.

The Souderton Area School District posted a notice on its website that its schools were on lockdown due to the police activity.

"All students are safe and are secured in their classrooms. Visitors will not be allowed in the schools until further notice," it said.

The first shooting was reported around 3:55 am (0855 GMT).

WPVI cited sources as saying all victims -- including at least one woman -- were shot at close range.

It was unclear whether the shootings were related or if there were other suspects.