Police say gunmen have shot dead three policemen who were manning a highway checkpoint in Nigeria's northeast.

Bauchi state police spokesman Hassan Auyo said the assailants injured a fourth policeman in the attack that occurred Thursday morning on a highway leading to the city of Bauchi.

He said they stole the policemen's rifles.

Auyo said police were still investigating the attack which comes days after a bomb hidden inside a wheelbarrow exploded near a beer garden in Bauchi, killing a 6-year-old boy.

Bauchi has previously been struck by sectarian violence sweeping across Nigeria's north from an Islamist insurgency. However, there was no claim of responsibility for the attack Thursday.