The shooting - which happened just before 9 a.m. (local time), less than one mile (1.6 kilometres) from police headquarters - comes amid spiraling tensions across the city - and the country - between the US black community and police.

US President Obama has called for restraint after three police officers were shot dead in the city of Baton Rouge in Louisiana, BBC reports.

The gunman, Gavin Long, an African-American who had served for five years in the Marines, was also killed. He had posted videos on the internet complaining about police treatment of African-Americans.

Tensions in Baton Rouge have been high since a black man, Alton Sterling, was shot dead by police two weeks ago.

Multiple police units were stationed at Our Lady of the Lake Regional Medical Center, where stricken officers were believed to be undergoing treatment at a trauma centre.

Police-community relations in Baton Rouge have been especially tense since the killing of 37-year-old Alton Sterling, a black man killed by white officers earlier this month after a scuffle at a convenience store.

The killing was captured on cellphone video and circulated widely on the internet.

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