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 fighters.
The explosion happened at about 9:00 a.m. local time, as primary school teachers and public sector workers were in line to pick up 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 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.
That bombing followed a twin attack on a mosque and restaurant in the central city of Jos on Sunday, which left 44 people dead, and a suicide bomb attack on a church in Potiskum that killed five.
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.
El-Rufai is urging citizens to avoid crowded public places including mosques and churches as armed group Boko Haram extend the breadth and tempo of attacks that have killed some 300 people in a week.
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 checks.
“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,” Abubakar said.
“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,” Abubakar added.
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 worship.
“Adequate security has also been ordered for venues where Muslims break [the Ramadan] fast in the evenings,” he said in a statement late Monday.
Arase also said street trading on roads in the capital Abuja had been banned, while unauthorized taxis and buses were not allowed to park in the center of the city.
Zaria has not been known as a stronghold of Boko Haram, which has been fighting for six years to create a hard-line state based on its own interpretation of Islamic law in northeast Nigeria, but it has been attacked before.
In March last year, a prominent Salafist cleric who had criticized the group was shot dead with his wife and son as he drove home from teaching a theology class.
A boarding school that he ran was previously hit by a bomb blast and gunfire in September 2012.
Zaria was also where a French engineer managed to flee his captors in November 2013 after being held for nine months by the Boko Haram offshoot Ansaru.
In June 2012, bomb blasts ripped through two churches in Zaria, killing several worshippers and injuring many others. Boko Haram claimed the attacks.