The Archbishop of Canterbury, Justin Welby, has been asked by the UN Secretary-General António Guterres to join a new, high-level advisory board on mediation.

Archbishop Welby, who has years of experience in the work of reconciliation, is one of 18 global leaders and experts who have been asked to form the board, which will provide the secretary-general with advice on mediation initiatives and back specific mediation efforts around the world.

As Guterres announced earlier this month, the establishment of the board is part of the 'surge in diplomacy for peace' he has advocated, and gives due priority to the prevention and mediation work of the UN.

Lambeth Palace said that the board is expected to allow the UN to work more effectively with regional organisations, non-governmental groups and others involved in mediation around the world.

The new board contains representatives from around the world, including the President of Chile, former President of Finland and former President of the Republic of Nigeria, and brings together an extensive range of experience, skills, knowledge and contacts to assist the secretary-general.

Archbishop Welby said on Twitter: 'Honoured to join UN Secretary General's board on mediation. Praying for its contribution to global peace and reconciliation.'

The appointment came as Donald Trump criticised the UN for bloated bureaucracy and mismanagement on his first visit yesterday to the UN headquarters in New York, calling for 'truly bold reforms' so it could be a greater force for world peace.

Ahead of his maiden speech to the annual UN General Assembly today, Trump said: 'In recent years the United Nations has not reached its full potential because of bureaucracy and mismanagement, while the United Nations on a regular budget has increased by 140 per cent and its staff has more than doubled since 2000.

'The United Nations must hold every level of management accountable, protect whistleblowers and focus on results rather than on process,' Trump added.

'I am confident that if we work together and champion truly bold reforms the United Nations will emerge as a stronger, more effective, more just and greater force for peace and harmony in the world.'