Nigerian forces say they have killed 52 Islamists, arrested 70 KANO, Nigeria (Reuters) - Nigerian security forces said on Saturday they had killed 52 Islamist militants over 10 days of fighting in the northeasterly Borno state, at a cost of only two of their own men, with no civilian deaths. The announcement came a day after President Goodluck Jonathan paid a visit to the state in which he rejected the idea of an amnesty for the Islamist sect Boko Haram, which has killed hundreds in gun and bomb attacks in the past two years. The Islamists are seen as the main security threat to Africa's top energy producer, although their sphere of influence is far from the crucial oil fields in the south. Lieutenant Colonel Sagir Musa, spokesman for the mixed military and police joint task force (JTF) in Borno state, said in a statement that a series of operations had been conducted against Islamists over the past 10 days. "During these operations under the period stated, there were exchanges of fire that led to the death of 52 Boko Haram terrorists including 10 commanders of the sect," he said. Seventy terrorists were also arrested. He said the JTF had also seized a number of weapons. It was not possible to verify the claims independently. Nigerian forces often claim substantial successes against Boko Haram militants but rarely admit to significant losses on their own side or civilian casualties during their operations. Residents of Maiduguri, Borno's largest city, say dozens of civilians die in military raids against Boko Haram, and rights groups accuse the JTF of heavyhandedness and extrajudicial killing. A Nigerian Islamist splinter group from Boko Haram, based in the northwest, said on Saturday it had killed seven foreign hostages seized last month from a construction firm's compound in northern Nigeria. Nigerian authorities said they had no information on any such killing, and doubted the veracity of the statement. Reporting by Chukwuemeka Madu; Writing by Tim Cocks; Editing by Kevin Liffey