Taoiseach Leo Varadkar has said he wants devolved government in Northern Ireland to last.
The Taoiseach was greeted by First Minister Michelle O'Neill and deputy First Minister Emma Little-Pengelly at Stormont Castle.
They had a meeting inside before Mr Varadkar met the rest of the newly-formed Stormont Executive.
Ms O'Neill and Ms Little-Pengelly welcomed the Taoiseach to the Executive table, before Ms Little-Pengelly said she looked forward to building a constructive relationship with the Taoiseach, "one based on mutual respect", adding as the closest neighbour, it "makes sense for us to have a constructive relationship - we haven't always had in the past".
Mr Varadkar said he was glad to be there, adding there were "various times over the past year or two I didn't think this day would happen".
"It's great that the institutions are back up and running again, we want the Executive to be a success and to last, and keen to help in any way we can but not to interfere, but definitely to help, and keen to see the North South Ministerial Council up and running again as soon as possible, and the British Irish Council as well of course," he said.
"We'll have the St Patrick's Day visits which I think will take on a much more positive feel because in the US they'll be keen to see the Good Friday Agreement institutions working and the main thing is to try and keep the lines of communication open."
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Mr Varadkar said that the purpose of his visit to Stormont was to congratulate the first and deputy first ministers and all who made possible in the new Executive.
He said he had a very good meeting with the British Prime Minister Rishi Sunak and his team this morning.
"We are keen to think about the future and work on north-south cooperation but also east-west cooperation, which is very important," he added.
Ms O'Neill said the new power-sharing Executive was presenting a "united front" in terms of Northern Ireland's financial situation.
She said: "Today is a good day, we have an Executive functioning, we have an Executive in place who want to tackle all the issues that we are trying to tackle.
"Emma and I stand in front of you today as First and deputy First Minister. We are trying to do our best to get to grips with some of these issues that we have ahead of us."
She added: "Let's for today focus on the fact that we have presented a united front in terms of the finance situation that we face here.
"We are about to start this Executive meeting and we are all going to work together to do whatever we can to secure the best possible financial situation that allows us to deliver good public services."
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Ms Little-Pengelly said Executive ministers had to work together to meet Northern Ireland's financial challenges.
She said: "Within every department there are very important issues.
"But the key thing here is we are only going to find resolutions for those by working together and working constructively together.
"That's what we're up for, I think the rest of the Executive is up for that challenge."
Mr Varadkar said that the priority for any new Executive or any government in any country has to be the day-to-day concerns of people.
He said that there were very long hospital waiting lists and issues around the economy and public sector pay.
The Taoiseach added that that he had the impression from the first ministers and Executive that they are keen to get stuck into their briefs and the day-to-day issues.
"I am confident that the institutions will last.. When the assembly falls, it tends not to be reestablished for years.
"I do feel a sense of confidence from the new executive that this is here to last."
On reform, he said that he felt that issue should wait a bit to allow the parties to do their work, to get to know their briefs, ministries and work together. He added that reforms have been made before, it can be done, but there should be a period of bedding down.
He added that Ireland intended to make further allocations using the Shared Island Fund over the course of the year.
"I'm very keen to coordinate that with the Secretary of State and the Executive now it's up and running," he said.
On the issue of a united Ireland, he said that was not for today (Monday), but rather it’s about marking the fact that the Good Friday Agreement, voted for in big numbers north and south, was functioning again through the Executive and north and south bodies.
He said that this was what the day should be about that rather than constitutional questions.