At least 20 people were killed when a bomb blast ripped through a government office in Zaria, northern Nigeria, on Tuesday, in an attack likely to be blamed on Boko Haram Islamists.
The explosion happened at about 9:00 am (0800 GMT), as primary school teachers and public sector workers were queuing for identity checks, according to witnesses.
“I am sad that a terrorist bomb attack just killed 20 people in Sabon Gari Zaria,” Kaduna state governor Nasir Ahmad El-Rufai wrote on his Twitter account.
But witnesses feared the death toll could rise further, describing how the building was packed with people at the time.
Zaria, a mainly Muslim city some 75 kilometres (47 miles) north of the state capital Kaduna city, is near the border with Katsina and Kano states.
On Monday night, a young girl believed to be aged just 13 was killed when explosives strapped to her body detonated near a major mosque in Kano city.
Boko Haram has increased the intensity and frequency of its attacks on civilians since President Muhammadu Buhari came to power on May 29 vowing to crush the rebels.
But he been unable to stem the bloodshed from guerrilla-style attacks on “soft” targets.
With the latest blast, nearly 550 people have been killed since Buhari’s inauguration, according to AFP reporting.
Local government worker Mahmud Abbas said public sector staff and primary school teachers were undergoing screening to identify potential ghost workers on the state payroll.
Another staff member who was waiting outside, Mohammed Abubakar, said: “We were taking turns going into the hall in batches for the screening and also to get our pay cheques.
“The first batch had gone in. There were almost 100 people there, including the staff, the screening committee and accountants from the banks.
“There was a huge explosion inside the hall followed by billows of smoke and dust. Now the area has been cordoned off by security men.
“I can’t give you an exact toll but I believe that dozens must have died given the number of people inside and the sound of the explosion.”
El-Rufai, from Buhari’s All Progressives Congress (APC) party, said people in Zaria should be vigilant and avoid crowded places such as mosques, churches and bus stations in the next few weeks.
“We call on our people to report any suspicious persons and movements to law enforcement agents, traditional rulers and religious leaders,” he added.
His warning followed a country-wide order from the federal police chief, Solomon Arase, to state commanders to increase security at all places of workship.
“Adequate security has also been ordered for venues where Muslims break (the Ramadan) fast in the evenings,” he said in a statement late on Monday.
Arase also said street hawking and trading on roads in the capital Abuja had been banned, while unauthorised taxis and buses were not allowed to park in the centre of the city.