The leader of Plaid Cymru is hoping to become Welsh first minister as early as Tuesday after his party won a historic victory in the Senedd elections, soundly beating Labour and holding off Reform UK.

Plaid fell short of winning a majority in the Welsh parliament but Rhun ap Iorwerth said on Sunday he hoped other parties would work with him and told UK Labour not to punish Wales over the result.

Asked on BBC Radio Wales when he hoped he would be elected as first minister, ap Iorwerth said: “We’re ready to go as quickly as we can. We hope for it to be Tuesday. If there’s a delay it won’t be much. We want to get going.”

Ap Iorwerth said Plaid had put a clear programme for government on the table that he hoped would get backing from across the Senedd. “We want actively to get support of people in other parties. I will be explicitly cooperative,” he said.

The Plaid leader said he had spoken to representatives from all parties, except for Welsh Reform leader Dan Thomas.

Labour was left with just nine seats in the Senedd, ending 100 years of dominance in Wales.

Ap Iorwerth said: “Labour can go in one of two ways now on a UK level. They can decide to punish Wales because Wales turned its back on Labour and say: ‘Right you’re getting nothing now.’

“In which case it’s difficult to see Labour planning any way back. Or they reflect and recognise the indifference shown by UK Labour leadership to Wales has to come to an end.”

Ap Iorwerth suggested he did not believe Keir Starmer would remain in Downing Street for long, saying: “I will guide the next UK prime minster, whoever that might be, to start looking at Wales in a different way.”

Asked if Wales may be treated differently if someone like Andy Burnham took over from Starmer, ap Iorwerth said: “I think you might be right. It is clear to me Keir Starmer has been getting it very very wrong in the indifference shown towards Wales. Keir Starmer can change his ways or Labour can choose someone else to do things in a different way.”

He also said he believed there could be cooperation with the other nationalist parties in Scotland and Northern Ireland. Speaking on BBC’s Sunday with Laura Kuenssberg, he said: “There are a number of different ways that we can work together. There are ways of looking at policies that we have in common, the way that we use the natural resources off our coasts, for example.

“But there’s a deeper sense than that, too, of being able to make a stand together to call for less inequality within these islands.”

Ken Skates, the interim leader of Welsh Labour after the former first minister Eluned Morgan resigned, said its members would meet on Monday to discuss how they would approach the vote on the next first minister but described the idea of his party teaming up with Reform to try to keep ap Iorwerth out as “deeply unpleasant”.

He said its relationship with Plaid would be “mature” but it would serve the people of Wales, not ap Iorwerth’s party.