Scotland must have more powers over welfare if it is to mitigate policies such as the so-called "rape clause", Nicola Sturgeon has said.

The First Minister responded to critics who have accused the SNP of using the controversial issue as a political tool in campaigning for the general election.

A report from the Scottish Parliament Information Centre (SPICe) found it would cost Scotland about £200 million over the next four years to mitigate the clause using Holyrood's new powers to top up benefits.

The policy, due to be debated by MSPs at Holyrood on Tuesday, is part of UK Government welfare reforms introduced in April which mean child tax credits are now capped at two children.

A clause in the new rules means mothers who have a third child as a result of rape can be exempted but would have to provide evidence in order to do so.

Speaking at the Scottish Trades Union Congress (STUC) in Aviemore in the Highlands, Ms Sturgeon said: "The SNP government has done a lot to try to mitigate Tory welfare policies but there comes a point where if we are going to be able to mitigate those policies then we need to have the proper powers and the budget transfer to do so, because where does it stop?

"The Tories just decide they're not going to pay any benefits to anybody in Scotland any more, pocket all the savings from that and say 'over to the Scottish Parliament?'

"It's a ridiculous proposition to say that the Scottish Government can simply step in, take money from elsewhere to mitigate Tory policies."

Responding to the argument her government had stepped in to mitigate the so-called bedroom tax, she added: "We will do that where we can.

"I'm saying there has to come a point where that is no longer feasible.

"So, if it's the case, if it's the Tory argument that the Scottish Government is better-placed to take these decisions, then let's have the full power over universal credit and let's transfer the budget as well.

"The Tories should transfer the savings they're making from the two-child tax policy and the rape clause, and then let us decide whether we want to save that money and spend it on something else, as they've done, or whether we want instead to keep spending that money on protecting household budgets.

"The rape clause is wrong in principle and it's not just wrong in Scotland, it's wrong across the UK as well, so the solution for the rape clause is for the Tories to repeal it, not for the Scottish Government to take money from schools and hospitals to plug the gap because they pocketed the savings."

Earlier, STUC president Helen Connor joined those speaking out against the policy.

Ms Connor said: "I tell you what slogan cannot be used in the next seven weeks - Trust Theresa.

"Trust the Tories - I don't think so. How can we trust her on employment rights? How can we trust her with our pensions? How can we trust someone who thinks it is right to have a rape clause in the welfare system?

"Shame on her and shame on Ruth Davidson, who has consistently refused to condemn it."