JOS, NIGERIA (CNN) - Three explosions rocked the city of Jos in Central Nigeria on Tuesday, two local journalists said.
The blasts caused casualties, but it was not immediately clear how many.
A journalist on the scene of the first explosion called it "massive." People were screaming and running, some covered in blood. Some had to be carried away, the journalist said.
An ambulance driver who asked not to be identified said he saw at least 15 bodies and about 30 injured at one of the blast sites.
In a statement, President Goodluck Jonathan condemned the bombings as a "tragic assault on human freedom" and described those behind them as "cruel and evil."
"President Jonathan assures all Nigerians that government remains fully committed to winning the war against terror, and this administration will not be cowed by the atrocities of enemies of human progress and civilization," the statement said, adding that Nigeria was committed to implementing anti-terrorism measures and resolutions put forth at a recent summit in Paris.
The first blast was a bomb detonated at the Terminus market, where food and clothes are sold, the journalists said. The second blast was at the same market and could have been a bomb or gas canister ignited by the first bomb.
The third explosion was at Abuja market, which sells shoes, the journalists said.
When CNN tried to speak with a nurse at a local hospital by phone, she was unable to hear because of victims' cries and screams.
Late Sunday, a bomb in the northern Nigerian city of Kano killed at least four people, according to local police.
The blast occurred at a busy intersection in a predominantly Christian area of the city and left several cars burning, Kano police spokesman Rabilu Ringim said. It was not immediately clear who was responsible for the attack, the spokesman said.
Terrorism in Nigeria has been in the spotlight recently since more than 200 schoolgirls were kidnapped by the militant group Boko Haram.
The terror group abducted 276 girls on April 14 from a boarding school in Chibok in northeastern Nigeria. Dozens escaped, but more than 200 girls are still missing.
In his statement Tuesday, Jonathan reaffirmed his government's commitment to take "every necessary measure" to find the girls and cooperate with other countries in the region to combat the "Boko Haram menace."
The president also said Nigeria was determined to ensure safety and security in schools in Borno state and other parts of the country and to rebuild the school in Chibok.