Leanne Wood: Plaid Cymru and Labour could form united alternative to Tories
New Plaid Cymru leader Leanne Wood has made an overture to the Labour Party to build a "united Welsh alternative" to the Conservatives.
She spoke as her party approaches its first test under her leadership in next week's local council elections.
Labour said Plaid supporters should send a message to the UK government in Westminster by voting Labour on 3 May.
In the BBC Wales interviews Ms Wood repeated opposition to working with the Tories.
She also explained why as a republican she turned down an invitation to a Diamond Jubilee service with the Queen in Cardiff on Thursday.
Labour and Plaid formed a Welsh government coalition after the assembly election in 2007.
Their One Wales pact lasted until last year's assembly election when Labour was returned to power, but without an outright majority in the Senedd chamber.
Her comments come as Plaid and Labour compete for votes at the local elections on Thursday, 3 May, particularly in places like Carmarthenshire and Caerphilly.
Ms Wood said Labour had "let people down", accusing the party of "inaction" and "a lack of ambition".
But she added: "Where Labour would be prepared to co-operate with us, where they are prepared to put forward progressive policies and where they are prepared to ditch tribalism and parochialism, we will look to work with Labour under those circumstances.
"But it is all about the kind of progressive politics that we can build. Can we build a united Welsh alternative to the Tories' cuts?
"I think we can, but that will involve people coming together with a positive attitude to do that."
In article published online on Tuesday, Ms Wood wrote about the two parties creating "a truly united and progressive civic force operating at all levels".
Coalitions with other parties have to be formed on the basis of "shared values", she told BBC Wales.
"We will form local coalitions and we will co-operate with anyone who shares our progressive values and our progressive agenda," she said.
"For me, that rules out the Conservatives. I don't see how anyone could argue that the Conservatives have Wales' best interests at heart.
"The cuts they are meting out from London now are affecting people in Wales worse than they are in other parts of the UK."
Plaid says the local elections come too soon into Ms Wood's leadership to be seen as a referendum on her. She was elected on 15 March.
"I've just come into post so I think it would be a big expectation to think that my leadership can drastically change the fortunes of Plaid Cymru," she said.
"I'm hoping that we can do well. Obviously we are going all out to win as many council seats as we can."
She added: "It's going to be a difficult election for Plaid Cymru. The British parties are very much trying to turn it into a British election."
A Welsh Labour spokesman said that if Plaid supporters want to "send a message" to the UK government they should vote Labour.
"On the doorstep it is Labour candidates that are leading the fight against Cameron's police cuts and against the millionaires' Budget," he said.
He added that Welsh Labour leader and First Minister Carwyn Jones had delivered on a pledge to set aside politics and work with opponents after last year's elections.
Ms Wood has turned down an invitation to attend a service with the Queen and Duke of Edinburgh at Llandaff Cathedral in Cardiff on Thursday, held as part of celebrations to mark the Diamond Jubilee.
Although she has said she will be present when the Queen opens the Welsh assembly, Ms Wood said that as a republican she could not attend Thursday's service and that "principles and honesty are important in politics".
At a press briefing, Plaid AM Rhodri Glyn Thomas said the party would be represented at the cathedral by its three previous leaders - Ieuan Wyn Jones, Lord Wigley and Lord Elis-Thomas.
Asked about Ms Wood's offer to Labour, he said: "I didn't hear that interview therefore I have no idea what Leanne was referring to."
Conservative assembly leader Andrew RT Davies said: "Leanne is marking out her territory obviously advocating independence for Wales (and) a more left-wing position than maybe the Labour Party would advocate. It's for her to mark out her territory.
"The Conservatives have championed Wales within the UK and have delivered for Wales... the question is almost what have Plaid Cymru ever achieved for Wales?"
Mr Davies cited electrification of the railway line from Paddington to Cardiff and the referendum on increased powers for the assembly as examples of the Conservatives delivering for Wales.