NIGERIAN gunmen killed 46 police officers in an ambush in the central state of Nassarawa this week, police said.
However, the governor there believed a lesser-known local cult was behind the killings and not Boko Haram Islamists.
Boko Haram has waged a three-year insurgency in Nigeria, although it and other Islamist groups tend to operate further north than Nassarawa. It is suspected of launching a deadly assault on the northeastern town of Bama, also on Tuesday.
President Goodluck Jonathan cut short his trip to South Africa and Namibia to return home on Thursday and oversee efforts to contain threats to Nigerian security, highlighted by this week's bloodshed.
"Forty-six police officers were killed about 10 km (6 miles) from Lafia by members of a militia who had ambushed them on their way to an operation to arrest the leader of the militia group," police spokesman Sergie Ezegam said.
Local media quoted Nassarawa State Governor Tanko Al-Makura as saying the attack was carried out by a cult called Ombatse, meaning "the time has come" in the local Eggon language.
The group has attacked officials, churches and mosques in the past, he said, but added that this week's assault signified a marked escalation in the scale of its operations.
"Two weeks ago, we discovered a certain militia group holding arms and carrying out cult activities in the state," Al-Makura was quoted as saying in local papers.
"Since January, this thing has not abated and in the past two weeks, it has taken on a totally different dimension."
Two security sources also said they did not think the attack on Nassarawa was carried out by Boko Haram. The Ombatse group is motivated by ethnic rivalries within the state, one security source said.
Boko Haram and offshoots such as the al Qaeda-linked group Ansaru, as well as associated criminal networks, are seen as the main threat to stability in Africa's top energy producer.
Although Boko Haram's attacks mostly occur in its northeast stronghold, its reach has grown in the last year, while Ansaru's attacks included a siege on a police barracks in the capital Abuja and violence further south.
Ansaru, dubbed a terrorist group by Britain, claimed responsibility for a January attack in Kogi state on a convoy of Nigerian soldiers en route to deployment with West African forces in Mali. Kogi is south of Abuja and borders Nassarawa.
Western governments are increasingly concerned about Nigerian militants linking up with other jihadist groups in West Africa.
Boko Haram wants to carve out an Islamic state in a country whose population of 170 million is split roughly equally between Christians and Muslims.
Around 200 heavily armed suspected members of the group laid siege to the northeastern town of Bama on Tuesday, leaving 55 people dead, the military there said.
Attacks by Boko Haram have killed more than 3,000 people since 2009, based on figures from Human Rights Watch.