Tánaiste and Minister for Foreign Affairs Eamon Gilmore has said he is "reasonably optimistic" the US Congress would pass immigration reform helping an estimated 50,000 Irish illegals.

Speaking on a visit to Washington for two days of meetings with members of Congress, Mr Gilmore said there has been “a momentum” to try to pass immigration reform. However, he added he did not want to overstate the prospect of it happening.

He said he knew the leadership of the Republican Party was "anxious" to change US legislation giving legal status to almost 12 million so-called 'undocumented" immigrants. As a result, he was concentrating his efforts during his visit on discussions with Republican Congressmen "in the hope that there will be agreement we hope sooner rather than later," he added.

A comprehensive bill passed by the Democrat-led Senate last year has stalled in the Republican-controlled House of Representative over the party's concerns about putting illegal immigrants on a path to citizenship before controls at the south-western US border with Mexico are tightened to prevent a flow of new illegal migrants.

Mr Gilmore said the defeat of Republican majority leader of the House of Representatives Eric Cantor in a primary election last week was "a setback" for the cause of immigration reform. "That has obviously slowed things down," he said.

On his last visit to the US before stepping down as Labour Party leader next month, Mr Gilmore met Congressman Paul Ryan, the 2012 Republican vice-presidential candidate, and Democratic Congressman Luis Gutierrez, a long-time champion of immigration reform, along with the "Friends of Ireland" group of congressmen on Capitol Hill.

Earlier, the Tánaiste laid a wreath at a memorial in the Congressional Cemetery on Capitol Hill to the 21 women and girls killed at the Washington Arsenal explosion during the US Civil War.

Mr Gilmore said their deaths 150 years ago this week is "a story that in Ireland we feel very closely to because so many of the women who lost their lives were Irish immigrants or were of Irish extraction".

They and their families “highlight yet again the long historical ties between Ireland and the United States”, he said.