Micheal Martin has spoken with new British Prime Minister Liz Truss.
The Taoiseach and Ms Truss talked over the phone about "common challenges" facing Ireland and the UK.
Mr Martin also offered the condolences of the Irish people to Ms Truss on the death of the Queen.
A spokesman for the Taoiseach said: "Taoiseach Micheál Martin and British Prime Minister Liz Truss spoke by phone this afternoon.
"The Taoiseach extended his sincere condolences to the UK Government, King Charles III and the Royal Family, and the British people on the loss of Her Majesty Queen Elizabeth.
"They reflected on her historic State visit to Ireland in 2011 and its contribution to advancing reconciliation and relations on these islands.
"The Taoiseach also offered his congratulations to the Prime Minister on her appointment, and told how he looked forward to working constructively with her.
"They discussed the illegal Russian invasion of Ukraine, their support for Ukraine, and recognised the substantive EU-UK cooperation as part of the global response. "They exchanged views on common challenges including soaring energy prices and the rising cost of living.
"They discussed a range of issues of mutual concern, including the Northern Ireland Protocol, and agreed to keep in close contact in the weeks ahead."
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