The Scottish Government has been slammed for "a betrayal" by opposition parties after announcing a three-year delay to the full devolution of a raft of welfare powers.

Social security secretary Shirley-Anne Somerville told MSPs that Scotland's new benefits agency Social Security Scotland would not be able to fully administer the 11 benefits until 2024 - not 2021 as planned.

Somerville's predecessor Jeane Freeman had previously pledged to implement the devolved powers, including over Personal Independence Payments (PIP) for disabled people, by the end of this parliamentary term.

Scottish Labour said ministers had "left vulnerable people at the mercy of the callous DWP and the Tories".

In a ministerial statement on Thursday, Somerville described the devolution of these powers as "the most complicated feat of devolution attempted since this parliament was reconvened".

Control of welfare payments worth around £3bn a year was part of the package of powers transferred to Holyrood in the wake of the 2014 independence referendum.

The UK's Department for Work and Pensions (DWP) is still administering a swathe of benefits despite the Scottish Parliament being able to legislate on them since last year, in a "split competence" arrangement.

Scottish Conservative welfare spokeswoman Michelle Ballantyne accused Scottish ministers of hypocrisy over the latest delay, after it was previously pushed back from 2020 to 2021.

She told MSPs: "For two years, the SNP has slammed the DWP, you have used highly charged language on the UK Government's administration of benefits, you have raised expectations and promised the earth to some of Scotland's most vulnerable people.

"After repeated promises that the new system would be up and running by the end of this Parliament, we now learn that it will be 2024 before (the Personal Independence Payment)'s successor is in place.

"And this is from the party that said it could set up an independent country in 18 months.

"Can the minister not see that this is deeply embarrassing? She must apologise to the Scottish DWP staff she has repeatedly denigrated".

Scottish Labour's social security spokesman Mark Griffin also urged Somerville to say sorry.

Griffin said: "The SNP Government has left vulnerable people at the mercy of the callous DWP and the Tories for far too long already.

"Ministers must apologise to everyone in Scotland entitled to social security who is being left at the hands of the Tories.

"Delaying full control of the powers until 2024 is a betrayal of vulnerable people who were told the Scottish Government would assume responsibility within this parliamentary term."

He added: "Today's announcement also fails to make any mention of the SNP's pledged income supplement.

"With almost a quarter of a million Scottish children living in poverty that just is not good enough."

Somerville said changes made to social security should not be rushed but conceded this would mean "difficult decisions on timing".

She told Holyrood: "The timescales I've set out remain very challenging and there are many unknowns, both within our work on social security devolution and beyond.

"We will therefore keep our plans under careful review and I will keep parliament updated on our progress.

"We shouldn't forget that we are the first government to begin the separation of a highly integrated welfare system between two countries.

"This cannot be done without taking difficult decisions on timing.

"But every day, as we break new ground, we gain more experience of how to accomplish the most complicated feat of devolution attempted since this parliament was reconvened."

The Scottish Government unveiled at the end of last year a new Best Start Grant for low-income families with new babies - the first to be wholly delivered by Social Security Scotland.