A blast on the outskirts of Nigeria's capital Abuja has killed at least nine people.
The explosion hit the satellite town of Nyanya, close to the site of a morning rush hour bomb attack at a bus station that killed at least 71 people on 14 April.
It comes as several May Day rallies were held across the country.
Many taking part in the march in Lagos were calling for the release of schoolgirls kidnapped by Boko Haram Islamists more than two weeks ago.
The mass kidnapping in the Chibok area of northeastern Borno state was one of the most shocking attacks in Boko Haram's five-year extremist uprising, which has killed thousands across the north and centre of the country.
Yesterday protesters held a "million-woman march" in Abuja over the government's failure to rescue the kidnapped schoolgirls.
Boko Haram has been resposible for violence over the past four years in its demand for Islamic rule in northern Nigeria.
US offers to help Nigeria in hunt for abducted girls
The US said it had offered Nigeria help in its search for the abducted girls.
"We have been engaged with the Nigerian government in discussions on what we might do to help support their efforts to find and free these young women," State Department spokeswoman Marie Harf told a daily briefing.
"We will continue to have those discussions and help in any way we can."
Ms Harf did not elaborate on the kind of assistance Washington is offering, but said: "We know Boko Haram is active in the area and we have worked very closely with the Nigerian government to build their capacity to fight this threat."
In 2012, the US provided over $20m in security assistance to Nigeria, part of that to build the country's military, boost its capacity to investigate terrorist attacks and enhance the government's forensic capabilities, she said.