Two civilians have died in an attack on a police station in the northern Nigerian city of Kano, police say.
A BBC correspondent says that gunmen stormed the station, throwing explosives and an hour-long shoot-out ensued.
The gunmen are suspected to be Islamist militants from Boko Haram, which recently carried out multiple bomb attacks in Kano, killing 185 people.
Police also say they shot at a bus near another police post on Monday.
There are no details of casualties in this early morning incident, which occurred near the same police station in the city's Mandawari area where an officer was killed on Friday night in another suspected Boko Haram attack.
The BBC's Abdullahi Kaura Abubakar in Kano says the Sunday evening attack on a police station in the Naibawa district, on the outskirts of Kano, happened just before the start of the dusk-to-dawn curfew.
"We are scared. The police and Boko Haram members are battling each other and there is gunfire everywhere," local resident Usman Ibrahim Bello told the Reuters news agency.
The curfew was imposed after the 20 January bombings - the most deadly since Boko Haram began its campaign of violence in 2009.
On Saturday, a Boko Haram spokesman rejected Nigerian President Goodluck Jonathan's recent call for open dialogue to end the conflict.
He said it was "impossible" to hold talks, after police said they had killed 11 militants in the group's base in the north-eastern city of Maiduguri over the weekend.
He also warned that if group members who had been captured in the north-western Sokoto state were not released, Kano-style attacks would be launched there.
Boko Haram - whose name means "Western education is forbidden" - wants to establish Islamic law in Nigeria.
It stepped up its attacks in 2011, targeting police headquarters and the UN in the capital Abuja.
In recent weeks, southerners, who are mostly Christians or animists, living in the north have been the targets of deadly attacks and thousands have fled their homes.
Nigeria, Africa's most populous nation is roughly evening divided between the mainly Muslim north and the south.