Gunmen opened fire on the convoy of one of Nigeria's most senior Islamic leaders in the northern city of Kano on Saturday, killing four people, although the Emir of Kano himself escaped unhurt, authorities said.
Violence has worsened in Kano, the north's main city, in the past week, with near daily attacks by Islamist sect Boko Haram against security forces.
A security source said three of the emir's palace guards and a local government official were killed. The source said Boko Haram militants were suspected of being behind the assault.
A spokesman for joint military and police forces in Kano Captain Ikedichi Iweha said the gunmen fired on Emir Alhaji Ado Bayero's own car but he was not hit.
"We are still chasing further details," the spokesman said.
Practicing a strict Wahabist brand of Islam modeled on the Afghan Taliban, Boko Haram are fiercely anti-establishment and often attack Islamic clerics, many of whom they regard as corrupt, self serving and insufficiently strict in their interpretation of the Koran.
The Emir of Kano is one of the two most senior Islamic traditional leaders in Nigeria, the other being the Sultan of Sokoto. The current emir has been on the throne for half a century.
In a separate attack in northwestern Kogi state, suspected Islamist gunmen opened fire on a convoy of troops leaving northern Nigeria en route to deployment with West African forces in Mali, killing two officers, the commander of their barracks Major General Alphonsus Chukwu told Reuters by telephone.
"They were on their way to Kaduna for airlifting to Mali. The terrorists killed two officers while eight were wounded," he said.
WAVE OF VIOLENCE
Saturday's attack was the latest in a spate of violent episodes in Kano, an ancient city that was once at the heart of the great caravan routes connecting West Africa's interior with the Mediterranean.
Nigerian forces killed two Islamist gunmen in a shootout and arrested five others after their checkpoint in Kano was attacked on Thursday.
Boko Haram killed hundreds last year in a campaign to impose sharia, or Islamic law, on religiously mixed Nigeria. Its deadliest single attack was in Kano last January, when attacks on multiple police stations left 186 people dead, most of them civilians.
The Islamists have forged links over the years with international jihadists in Mali and Niger, including al Qaeda's north African wing, whom French and West African forces are fighting in northern Mali.
Nigeria plans to deploy around 1,200 troops as part of a West African intervention force, and officials fear Nigeria's involvement could further inflame its own Islamist insurgency.