The Sinn Féin leader has arrived in the US for a series of meetings in Washington DC and New York.

Mary Lou McDonald said she will brief members of the US Administration and senior congressional leaders about concerns that the British government will breach the Stormont House Agreement on dealing with the past and will also unilaterally trigger Article 16 of the Northern Ireland Protocol.

"Boris Johnson's Tory government is threatening to breach two international agreements; something which could have serious repercussions for everyone on the island of Ireland," Ms McDonald said.

"Because of the seriousness of the situation, I am travelling to the United States this week to brief the Administration and senior political leaders on Capitol Hill including the Majority Leader in the Senate Senator Chuck Schumer, Chair of the Ways and Means Committee Representative Richard Neal and Chair of Senate Foreign Relations Senator Robert Menendez," she added.

Ms McDonald will also meet the Congressional Friends of Ireland Caucus, senior trade union leaders and she will deliver an address on Brexit to the New York Bar Association.

Meanwhile, Ulster Unionist Party leader Doug Beattie is also in the US this week for meetings in New York and Washington.

He will hold talks with senior members of the US Congress and with officials from the Biden Administration.

"It is time unionism began promoting who we are and what we stand for. We must be more positive and less negative," Mr Beattie said.

"We must stop being overly confrontational and be more strategic in our thinking and that means creating unionist friends in the US," he added.