Security around Nigeria’s capital has been tightened the day after a car bomb exploded at the United Nations’ main headquarters in Abuja, killing at least 18 people in one of the deadliest assaults on the international body in a decade.

The United Nations is a disaster waiting to happen – a potential towering inferno that could be as devastating for workers, staff and visitors as the terror attacks on the World Trade Center’s twin towers, a US senator has said.