Royal Dutch Shell and the families of Ken Saro-Wiwa, an executed Nigerian opposition leader, and other activists hanged by the military government in 1995, on Monday agreed a $15.5m settlement in a New York court case stemming from allegations the oil group was complicit in the executions.

The settlement, in which Shell and its Nigerian subsidiary denied any liability, ended a 13-year campaign by relations and supporters of Saro-Wiwa to hold the company accountable.