A gunman has killed four US Marines and injured several others at two US Navy buildings in Chattanooga, Tennessee.

A local district lawyer said the shootings were being investigated as an "act of domestic terrorism".

The gunman, who was shot dead, was named as 24-year-old Mohammad Youssuf Abdulazeez by the FBI and local reports said he was born in the Middle East.

President Barack Obama said the attack was "heartbreaking" and said the suspect appeared to be a "lone gunman".

Abdulazeez is believed to have been born in Kuwait, but has lived in the US for several years.

He was arrested earlier this year in Chattanooga for driving under the influence of alcohol.

A spokesman for the University of Tennessee at Chattanooga said a student with the same name graduated in 2012 with a degree in engineering, according to local media reports.

The Chattanooga Times newspaper reported that he went to a local high school and competed on the wrestling team.

He left this message in his school yearbook: "My name causes national security alerts. What does yours do?"

Source: BBC