London - Archbishop of Canterbury Justin Welby warned on Sunday of the difficulties of negotiating with an "utterly merciless" group like Boko Haram, but called for active contact with the Nigerian Islamists over their abduction of scores of schoolgirls.
Welby has experience of negotiating with violent groups in the Niger Delta in southern Nigeria, and with a predecessor to Boko Haram around Maiduguri, the capital of northeastern Borno state where the group started out.
In an interview with BBC radio about the fate of more than 200 schoolgirls seized by the Islamist group last month, the archbishop said the girls faced a "colossal" risk.
"They're in the hands of a very disparate group which is extremely irrational and difficult to deal with and utterly merciless in the example it's shown in the past, and it must be a huge concern," he said.
Asked if it is possible to talk to groups like Boko Haram, he said: "They're in many layers. You have a very, very difficult inner core. and I think negotiation there is extremely complicated, though it needs to be tried.
"Then it goes out and out in different layers of commitment and understanding and involvement.
"There needs to be active negotiation, active contact with all the different layers."
He said Boko Haram has "always been a mixture of groups united as much by a common enemy as by a common cause".
Supporters turn to them because of immense poverty, high youth unemployment and the group's promises of social change delivered through the barrel of a gun, he said.
Welby, a former oil executive who joined the Church in his 30s, was careful not to criticise too strongly the response of the Nigerian government security forces.
The leader of the world's Anglicans noted their loss of control over large parts of northeastern Nigeria, despite a huge commitment of force.
"There needs to be effective police and security action across that area, and that is a huge challenge for the Nigerian government and one that we should not underestimate," he said.
He added: "We're talking about a massive area and a longstanding history of ethnic difference, of conflict with other Muslim groups."
Asked about allegations of human rights abuses by the military, he said he had no firsthand evidence but viewed the reports "with great concern".
He also said that it was "always a worry" that more Christians in Nigeria might take up arms to defend themselves against the group.
"They have a right to defend their lives and the lives of their children and their families," he said.
"But at the heart of Christian teaching is the example of Jesus who said forgive your enemies and forgave his own enemies on the cross."