The crisis in strife-torn Burundi risks spiralling into a "catastrophe' for the country and the wider region, the African Union warned on Sunday, after the killing of a senior military official amid escalating unrest. Unidentified gunmen killed Colonel Jean Bikomagu, a former chief of staff, outside his home in Bujumbura on Saturday. It was the second high-profile assassination this month as the fallout from the re-election of President Pierre Nkurunziza worsened in the central African nation.Nkurunziza was declared winner of elections held in July, for a third term that both opponents and Western powers said violated the constitution and provisions of a peace deal which ended a 1993-2005 civil war between the Hutu majority and Tutsi minority.Neighbouring Rwanda, which shares a similar ethnic population and where a 1994 genocide killed 800,000 people, has also expressed its concern over the unrest.In a statement, AU Commission chairwoman Nkosazana Dlamini-Zuma condemned Bikomagu's killing.Zuma "underlines that this ignoble act and many other violent acts in Burundi these last few months illustrate the gravity of the situation and the real risk of further deterioration with catastrophic consequences for the country and the whole region," the statement said.Bikomagu was army chief during the civil war that started in 1993 when the Tutsi-dominated army was fighting Nkurunziza's CNDD-FDD Hutu rebels.The election-related violence has been especially frequent in the capital Bujumbura, where the sound of gunfire is regularly heard at night.The Geneva office of the United Nations High Commissioner for Human Rights said last week that at least 96 people had been killed since the start of election-related unrest in April and urged leaders to renounce violence and resume their political dialogue.Zuma "insists once again on the imperative of dialogue and consensus to work for a peaceful and durable solution to the crisis and to preserve the important points in the 2000 Arusha Accord," the statement said.Burundi's security council, headed by Nkurunziza, said late on Saturday that it has asked for rapid investigations and the arrest and trial of the perpetrators behind the recent killings...