The leader of Sinn Féin has warned that there will be international consequences for the UK government if it walks away from the Northern Ireland Protocol.

Mary Lou McDonald was speaking in Washington and was giving her reaction to a report in the Financial Times that the US has delayed the lifting of UK steel and aluminium tariffs amid concerns over threats to invoke article 16 of the Protocol.

Ms McDonald said that after her meetings with US officials and congressional leaders, it was clear that the US will not tolerate the UK dispensing with the protocol.

Mary Lou McDonald speaking to RTÉ News in Washington

"There is no doubt where the United States stands on this issue. If Boris Johnson believes he can walk away from the Protocol he is wrong and there will be consequences internationally for Britain if he chooses that reckless course of action," she said.

Meanwhile, asked about a recent Sinn Féin golf fundraising event that was held in New York, Ms McDonald said the money was raised in and will be spent in the US and that it is a positive reflection of the level of interest in Ireland that exists in America.

She was delivering an address at the National Press Club in Washington and said that within the next five to 10 years she believes there will be referendums on the reunification of Ireland.

"We are on the threshold of writing the next chapter of Irish history," she said.

Ms McDonald met the majority leader in the Senate Chuck Schumer, Chair of the Ways and Means Committee Richard Neal, Chair of the Senate Foreign Relations Committee Bob Menendez and the Congressional Friends of Ireland Caucus.

"I've had very fruitful and very important conversations with senior figures in the Senate, Congress and the administration and the message is loud and clear that internationally people stand by the Good Friday Agreement. Nobody wants to see an amnesty; everybody wants to see all victims of the conflict treated fairly and within the law," Ms McDonald told RTÉ News.

"There is a conversation that is live now in respect of Irish reunification - the holding of referendums but more importantly the need to prepare for change," she added.

"I feel very reassured that we continue to enjoy the support of key figures, influencers and the administration here in Washington when it comes to protecting the Good Friday Agreement and protecting Irish interests."

The Sinn Féin leader will travel to New York where she will deliver an address on Brexit to the New York Bar Association.

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Ms McDonald welcomed the fact that the Ulster Unionist Party leader Doug Beattie is also in the US this week.

He has held talks with senior members of the US Congress and with officials from the Biden Administration.

He told RTÉ News that it was important to reach out to find friends beyond Irish shores and portray unionism in a positive light with less negativity and pessimism.

Doug Beattie is also in the US this week for meetings

"We can't blame the US if they don't understand the messages we are trying to convey and the concerns we are trying to raise because we are the ones who haven't been engaging, that's our fault," Mr Beattie said.

"Sinn Féin and nationalism have been far better at it than we have but this is the start of a process and I intend to come to the US at least twice a year to engage, outline problems and concerns and discuss what we can do to make Northern Ireland a better place remaining within the United Kingdom and address problems and misconceptions about things like the Protocol," he added.

The UUP leader said he told US officials that it was a "feast or a famine" for businesses in Northern Ireland because of the Protocol with some left struggling to survive.

"We also made a strong representation that the Protocol does not protect the Belfast/Good Friday Agreement but in fact it damages that fine balance that we as a party helped negotiate in 1998," Mr Beattie said.