Lassa fever has killed 142 people in Nigeria since the start of the year, the Nigeria Centre for Disease Control (NCDC) said on Thursday, reporting a rise of 32 fatalities in a month.
"Since the onset of the 2018 outbreak, there have been 142 deaths," it said.
Cases have been recorded in 20 of Nigeria's 36 states, it said.
"Eight states have exited the active phase of the outbreak while 12 states remain active," it said.
On March 6, the NCDC reported 110 deaths in 18 states.
Last month the World Heath Organisation (WHO) said the epidemic had reached record highs and promised to support efforts to contain it and treat those affected.
The NCDC said the southern states of Edo, Ondo and Ebonyi were worst-hit.
"WHO and NCDC have scaled up response at national and state levels," it added.
Lassa fever belongs to the same family as Marburg and Ebola, two deadly viruses that lead to infections with fever, vomiting and in worst-case scenarios, haemorrhagic bleeding.
The name comes from the town of Lassa in northern Nigeria where it was first identified in 1969.
The virus is spread through contact with food or household items contaminated with rats' urine or faeces or after coming into direct contact with the bodily fluids of an infected person.
It can be prevented by enhanced hygiene and avoidance of all contact with rats.
More than 100 people were killed in 2016 in one of the nation's worst outbreaks of the disease, affecting 14 states, including Lagos and the capital Abuja.