MAIDUGURI - Four more girls kidnapped by Boko Haram militants last month have escaped their captors, the education commissioner for Nigeria's Borno state said on Wednesday, leaving 219 still missing.The girls were taking exams at a secondary school in the remote northeastern village of Chibok on April 14 when the Islamist gunmen surrounded it, loaded 276 of them onto trucks and carted them off, according to official figures. Fifty-three escaped shortly afterwards, say authorities in Borno state, which lies at the epicentre of the insurgency.Education commissioner Musa Inuwa declined to give further details of the escape of the four. The girls' abduction shone an international spotlight on the the militants, whose violent struggle for an Islamic state in northern Nigeria has killed thousands and turned them into the biggest threat to security in Africa's top oil-producing state.From being a religious movement opposed to Western culture - Boko Haram means "Western education is a sin" in the northern Hausa language - the sect has emerged as a well-armed insurrection with a growing thirst for blood.Chief of Defence Staff Air Marshal Alex Badeh said on Tuesday the military knew where the abducted girls were but ruled out a rescue by force for fear of endangering them. Most officials think any raid to rescue them would run a high risk that the girls would be killed by their captors - Boko Haram has repeatedly showned ruthlessness in targeting civilians. WASHINGTON, May 27 (Reuters) - The United States said on Tuesday it does not have information that would support Nigeria's claim that it knows the whereabouts of more than 200 kidnapped schoolgirls, and US and European officials voiced skepticism about the statement."We don't have independent information from the United States to support" that statement, US State Department spokeswoman Jen Psaki told reporters. "We, as a matter of policy and for the girls' safety and wellbeing, would not discuss publicly this sort of information regardless." Nigerian Chief of Defence Staff Air Marshal Alex Badeh said on Monday that the country's military knew the location of the schoolgirls, abducted by the Boko Haram Islamic militant group on April 14.Five US and European security officials, who spoke on condition of anonymity, said they had no credible information on the location of the girls and were skeptical that the Nigerian government knew where they were. The five officials said the United States and some European allies had provided technical intelligence, including information from spy aircraft and satellites, to Nigerian authorities, who lack such intelligence capabilities.But the officials said that as far as they knew technical intelligence systems had not produced precise or credible information establishing the girls' location. The five officials said that if the Nigerians had obtained such information from informants on the ground, it has not been shared with US and allied agencies.One impediment to finding the girls, the officials said, was that since their abduction seven weeks ago they had been divided into small groups. Boko Haram is also believed to be hiding them in densely forested terrain where it would be hard for modern technical intelligence systems to gather information.