Brexit undermines the Good Friday Agreement according to Sinn Fein.

It comes as the man who brokered the deal says Britain's decision to leave the EU adds to the challenge of peace-making in Northern Ireland.

Former US senator George Mitchell believes it may reduce further co-operation. 

Sinn Fein is calling on the Irish government to act in the best interests of all citizens during Brexit negotiations.

Voters in the North take to the polls for the Assembly elections this week -

and Sinn Fein TD Pearse Doherty says concern is growing as Brexit approaches: