Sinn Féin has held a virtual meeting with members of the US Congress.
Party leader Mary Lou McDonald briefed the Congressional Friends of Ireland Caucus on Brexit and on the British government's plan to end prosecutions for killings during the Troubles in Northern Ireland.
She told the meeting that Britain had shown contempt for the rights of citizens in Ireland, their obligations under international agreements and the views of US political leaders.
"The proposals by the British government to close down investigations into their past actions and offer amnesties to their military is opposed by all parties, victims' groups, and the Irish Government," Ms McDonald said.
She also accused the British government of continuing to refuse to honour its obligations on Brexit and of creating uncertainty for business.
"By working together, we can ensure that the British government implements in full their commitments. The US remains a strong partner for peace, progress and prosperity in Ireland," she said.
Northern Ireland Secretary Brandon Lewis was due to visit Washington this week to hold meetings with members of Congress but the trip was cancelled for coronavirus reasons.
The Congressional Friends of Ireland Caucus is expected to hold an in-person meeting with Mr Lewis in autumn when he is able to travel to the US.