At least 20 people have been killed in a bomb blast in the city of Zaria, northern Nigeria, a regional governor and two workers said.
"I am sad that a terrorist bomb attack just killed 20 people in Sabon Gari Zaria," Nasir Ahmad El-Rufai, the governor of Kaduna state, wrote on his Twitter account on Tuesday.
"We call on our people to report any suspicious persons and movements to law enforcement agents, traditional rulers and religious leaders," El-Rufai also wrote on Twitter.
"The explosive went off at about 9am (08:00 GMT)... The area has been taken over by security personnel but high casualties are likely," local government worker Mahmud Abbas told the AFP news agency.
Zaria is located about 75km from the capital Kaduna city in the north of Kaduna state, not far from the border with Katsina and Kano states.
There was no immediate claim of responsibility but Zaria has been attacked before by Boko Haram fighters, who have increased their attacks on civilians in the last month.
Late on Monday night, a young girl believed to be just 13 was killed when explosives strapped to her body detonated near a major mosque in Kano city.
The explosion came a day after another suicide bomber blew himself up at a church in the city of Potiskum, Yobe state, killing five people and a twin attack in the central city of Jos that killed 44.