A newly banned Shiite group in northern Nigeria said on Thursday it was appealing in court against the government decision that observers are warning could spark sustained violence. The Islamic Movement in Nigeria said the ban by Kaduna state officials violates Nigerians’ rights to religious freedom. The ban, announced earlier this month, was made official by its publication on Wednesday. Tensions with the Shiite population are high after the army gunned down more than 300 people in an attack in December on the Islamic Movement in Nigeria’s headquarters. The government has said the group provoked the attack, with the military accusing it of trying to assassinate the country’s army chief. A claim that human rights groups have called unbelievable.