The Welsh First Minister said he has a “Celtic alliance” with his counterpart in Scotland, as he visited Glasgow for the Commonwealth Games.
Rhun ap Iorwerth said Plaid Cymru worked closely with John Swinney’s SNP.
He also said he is “optimistic” following his meeting with Prime Minister Andy Burnham on Thursday.
The pair discussed Mr Iorwerth’s request for further devolution for the Senedd.
Mr Iorwerth’s party won May’s election in Wales and, with an SNP win in Scotland and Sinn Féin holding the First Minister role in Northern Ireland, all of the UK’s devolved nations have independence-supporting parties in power.
The Welsh First Minister spoke to BBC Radio Scotland’s Breakfast programme on Friday.
Asked about the relationship between nationalist parties in Scotland, Wales and Northern Ireland, he said: “I think we have a Celtic alliance. I work closely with John Swinney…
“I have a good relationship. My party and the SNP were often referred to as sister parties.
“We have worked together at Westminster for many years prior to devolution, and we work closely now.”
The Welsh First Minister was also asked abut his strategy should Mr Burnham refuse to grant further powers to the Senedd.
However, he declined to “look forward” and instead said he wanted to “concentrate for the time being, on the fact that I believe I do have the potential of having a constructive relationship with a new UK Prime Minister that could lead us to a better place.”
He continued: “I am optimistic. I’m an optimistic man anyway.
“But I think the reason I take heart at this point in time on the question of further devolution for Wales, is that we have a Prime Minister now that has worked within a devolved context in Manchester, has understood the need to get devolution right.”
The Prime Minister met both first ministers in Glasgow before they all attended the opening ceremony of the Commonwealth Games at the Hydro arena.
Mr Iorwerth said he “particularly loved that spine-tingling rendition of 500 Miles” performed at the ceremony.
A Downing Street spokesperson said earlier: “The Prime Minister set out his commitment to working co-operatively with the Welsh Government, and to a relationship built on mutual respect.
“They discussed their shared ambition for growth and investment to reach every part of Wales.
“The Prime Minister said No 10 North would pay a pivotal role working with the Welsh Government, reflecting that he and the First Minister should work in tandem to deliver for people and communities.
“The Prime Minister said he wanted an open and ongoing dialogue with the First Minister on the issues that matter most across Wales.
“He looked forward to continuing that conversation in the months ahead.”
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