Kasala police chief Yahi Sulayman said it took place when worshippers had gathered for evening prayers in a mosque in the city of Kassala, which borders Eritrea.

“Three people have been killed and several wounded,” Sulayman said.

A medic at a hospital where the wounded were brought said they had been stabbed.

Residents said the attacker had tried to address worshippers who refused to listen to him and then started stabbing them.

“People in the mosque then retaliated and killed the attacker,” Sulayman said, adding that the identity of the attacker had not been established.

Since January Sudan has shut its eastern border with Eritrea, days after Khartoum declared an emergency in the state of Kassala.

Officials say the decision to declare emergency was part of a government campaign to collect illegal arms in the state.

Hundreds of Sudanese soldiers have been deployed in Kassala in recent months, residents say.

Thousands of Eritreans, fleeing a repressive regime at home, cross into Sudan illegally through the border with Kassala every year and later make perilous voyages across the Mediterranean to Europe.

Apart from Kassala, a state of emergency is in place in Sudan’s war-torn region of Darfur, as well as the states of Blue Nile, South Kordofan, and North Kurdufan.