By Lanre Ola and Kwasi Kpodo
MAIDUGURI, Nigeria/ACCRA May 30 (Reuters) - Suspected members of the Boko Haram Islamist group, which kidnapped 276 schoolgirls last month, gunned down a traditional Muslim emir in an attack on a convoy in northeastern Nigeria on Friday, the Borno state government said.
The Emir of Gwoza, Alhaji Idrissa Timta, was travelling with the emirs of Uba and Askira to a attend a funeral when the suspected Islamist gunmen opened fire on their car in Zhur, a remote community in Borno state.
Since April 14, when the girls were taken, at least 500 civilians have been killed by the militants, according to a Reuters count.
Timta died from gunshot wounds and two policemen were killed while the other two emirs managed to escape, a source at the Emir of Uba's palace told Reuters, requesting anonymity.
"The Emir of Gwoza was killed around 9 a.m. today following a bloody attack by some gunmen believed to be members of the Boko Haram," Borno state government said in a statement.
Sources had earlier told Reuters two of the traditional leaders had been kidnapped, but the palace source said the emirs of Uba and Askira had simply hidden for some time in the bush, leading to fears they had been abducted.
Most of the vehicles in the convoy were destroyed, the source said.
Friday's attack came as leaders from the 15-member Economic Community of West African States (ECOWAS) met in Ghana to discuss worsening insecurity in northern Nigeria and in Mali, where Tuareg separatists routed government troops last week.
"We must act, and we must put in place measures that make clear that we will not allow any of our countries to be used to destabilize other nations," Ghana's President John Dramani Mahama, who holds the rotating presidency of the bloc, said at the opening of the summit.
"ECOWAS must play a leading role in the effort to fully restore peace and security to the subregion and by so doing safeguard our future," he said.
Nigeria's head of counter-terrorism on Friday accused neighbouring Cameroon, which is not an ECOWAS member, of failing to make a serious effort to drive Boko Haram insurgents from its territory.
Despite a year-long military offensive against it, Boko Haram, which is fighting to reinstate an ancient Islamic caliphate in northern Nigeria, has been able to run riot in the north east and bomb cities across the country.
On Thursday, in the northeastern village of Gurmushi, near Nigeria's border with Cameroon, suspected Islamist gunmen riding motor bikes killed 32 people.
Nigeria's president Goodluck Jonathan said on Thursday he had ordered a full-scale operation against Boko Haram and sought to reassure parents of the 219 schoolgirls still being held by the group that their children would be freed.
Boko Haram has been kidnapping schoolgirls and forcing them to become "brides" for commanders for more than a year, but the attack on Chibok last month shocked the world and prompted an international effort to free them. (Writing by Tim Cocks, Bate Felix and Joe Bavier; Editing by Daniel Flynn and Stephen Addison)