Senedd CymruRhun ap Iorwerth became Wales' first minister in May after Plaid Cymru became the country's biggest partyWales' first minister Rhun ap Iorwerth has called for a "new relationship" between his country's government and Westminster following Sir Keir Starmer's resignation.
Ap Iorwerth spelled out a list of demands from the prime minister's successor including more powers for the Welsh government, and said the ability of his administration to engage had been hampered by turmoil in UK politics.
Welsh Labour MPs told BBC Wales that Sir Keir, who announced on Monday that he remain in post until a new Labour leader is selected by the party in September, had done the right thing.
Interim Welsh Labour leader Ken Skates praised the prime minister and said he had brought his party "back from oblivion".
But Reform's Welsh leader Dan Thomas called for a general election, saying: "The public must decide who governs the country, not Labour members."
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After ap Iorwerth's Plaid Cymru toppled Welsh Labour in May's historic Senedd election, Sir Keir promised a meeting with the first ministers of Wales, Scotland, and Northern Ireland in June, but it has failed to materialise.
After the prime minister's resignation, ap Iorwerth said he was "disappointed" that the Welsh government's ability to engage with the prime minister had been "hampered by the turmoil in Westminster".
In a statement, he said: "I wish Sir Keir Starmer well as he prepares to leave office. I would like to see his successor recognising that Wales needs a new relationship with Westminster, with a focus on greater powers, fair funding, and respect for the democratic mandate delivered by the people of Wales.
"My government and I will always seek a constructive relationship with whoever is in Number 10, but we have clear expectations that the respect agenda must work both ways."
Plaid had promised at the Senedd election to negotiate further powers and cash for Wales, with many of the demands shared by Welsh Labour members in the Senedd, such as the devolution of justice.
But none materialised under Sir Keir's tenure as prime minister.
Watch: Keir Starmer's resignation speech - in fullWelsh Labour MPs Tonia Antoniazzi and Ruth Jones told BBC Wales they both thought Sir Keir had "done the right thing".
One Labour minister who did not wish to be named said "many" in the UK government had wanted Sir Keir to announce his departure.
"It's never pleasant and sad for him personally, but the most important thing is to do what is best for the country - and this is," they said.
Former first minister Mark Drakeford said he hopes Manchester mayor Andy Burnham will become prime minister, having campaigned together in the recent Makerfield by-election which saw Burnham elected as an MP.
"I think he has an ability to persuade people in this country to have some hope again about the future," Drakeford said.
"People have lost faith in the possibility of improvement."
He said Burnham, who has announced he will stand to replace Sir Keir, has "seen devolution from both ends of the telescope" and had "run a major local authority, and has seen devolution from that local perspective as well".
But another Welsh Labour source added that while Burnham would need to engage with the Welsh government "in a positive and proactive way", he "also needs to be unafraid of calling them out".
"Right now the Welsh government has a shopping list significantly larger than its wallet," the source said, saying he would need to help the government prioritise the cost-of-living crisis.
PA MediaSir Keir announced a timetable for his exit from 10 Downing Street on MondayWelsh Secretary Jo Stevens described Sir Keir as "a man of dignity, duty, and commitment to our country and our party".
She said the prime minister "through sheer hard work, bravery and determination, he transformed our party, rebuilt public trust and led us to the greatest election victory in my lifetime."
Interim Welsh Labour leader Skates said Sir Keir had "brought our party back from oblivion and delivered one of the greatest victories the Labour Party has seen", noting his delivery of an increase to the minimum wage and announcement of £14bn for rail in Wales.
"He has led the country through exceptionally tough times with dignity and authenticity, and I want to put on record my deepest thanks to him," Skates said.
Welsh Liberal Democrat MP David Chadwick said a change in prime minister "won't change much unless Labour finally confronts the structural problems that continue to hold Wales back".
Welsh Conservative Senedd leader Darren Millar said despite Sir Keir's exit "Labour's failures do remain".
"The very last thing that Wales and the rest of the United Kingdom needs at this moment time is another Labour leader who won't stand up to Labour MPs on welfare, energy, defence spending and action on the cost of living," he said.
WalesKeir StarmerWelsh governmentRhun ap IorwerthUK governmentPlaid Cymru
