|Jonathan wants to bring the perpetrators of Friday's explosions to justice, but no arrests have been made so far [EPA]
Police have arrested six people in connection with deadly unrest following a series of bombings that killed 32 people in central Nigeria.
Abdurrahman Akano, Plateau state police chief, said on Monday that the suspects had participated in street violence on Sunday that left at least three dead and dozens wounded.
He also confirmed that no arrests have yet been made in connection with the Christmas Eve explosions.
Angry youths had barricaded roads and attacked passersby. They also set houses and a lorry ablaze, making it the worst episode of violence in the region in months.
Military patrolled the streets of Jos, Plateau state's main city, on Monday and security officials cordoned off the areas where the violence had erupted.
It was not immediately clear whether the Christmas Eve attacks had a religious motive.
Two of the bombs went off near a large market where people were doing last-minute Christmas shopping.
A third hit a mainly Christian area of Jos, while the fourth was near a road that leads to the city's main mosque.
Police and the army have declined to identify the bombing suspects. David Jang, the state governor, said that "we believe some highly placed people masterminded the attack".
The explosions in Plateau state came on the same day that members of Boko Haram, a Muslim sect, were accused of attacking two churches in the northern city of Maiduguri, killing at least six people.
Police have not confirmed if the bombings were related to the church attacks. The two areas are about 520km apart.
Boko Haram means "Western education is sacrilege" in the Hausa language.
It was thought to have been defeated in 2009 when the military crushed its mosque into concrete shards, and its leader was arrested and died in police custody.
Ban Ki-moon, United Nations secretary-general, has condemned the violence in Nigeria "especially at a time when millions of Nigerians are celebrating religious holidays".
Goodluck Jonathan, the Nigerian president, has expressed his sympathy to the victims' families and committed to bring the perpetrators to justice.
"I assure Nigerians that government will go to the root of this," he said of the explosions. "We must unearth what caused it and those behind it must be brought to book."
Religious violence has already left more than 500 people dead this year in Jos and neighbouring towns and villages.
But the situation was believed to have calmed down before the weekend bombings.
The explosions on Friday were the first major attack in Jos since the state government lifted a curfew in May.
The curfew had first been imposed in November 2008 during post-election violence.
It was then extended in January following clashes between Christian and Muslim groups.
More than 300 people, mostly Muslims, were killed in the January violence in Jos and surrounding villages.
Nigeria, a country of 150 million people, is almost evenly split between Muslims in the north and the predominantly Christian south.
The blasts happened in central Nigeria, where dozens of ethnic groups seek control of fertile lands.
The violence, though fractured across religious lines, often has more to do with local politics, economics and rights to grazing lands.
The government of Plateau state is controlled by Christian politicians who have blocked Muslims from being legally recognised as citizens.
This move has left many out of sought-after government jobs in a region where the tourism and tin mining industries have collapsed in the last decades.