President Samia Suluhu Hassan said on Twitter that the attacker was "neautralised" and "calm has returned".

“I send my condolences to the police service and the families of three policemen, and one officer of the SGA security company, who lost their lives after an armed person attacked them in the Salenda area of Dar es Salaam,” Hassan said.

The motive behind the attack is still unknown, police said, adding that the efforts to identify the attacker are on, according to an Al Jazeera report.

Officials said at least six people have been injured in the attack, it said.

The assailant was shot down while he was standing in the middle of the road. According to the onlookers, he was shouting that he wanted to kill police officers, said the report.

On Wednesday, President Samia Suluhu Hassan addressed security officials in another part of the city, Tanzania’s commercial hub. The attack happened shortly after the event.

The US Embassy warned citizens in a security alert to avoid the area.