Nicola Sturgeon is facing calls from campaigners to introduce a new benefit to tackle child poverty three years earlier than the Scottish Government has planned.

The First Minister has been told "kids can't wait" for the introduction of a new income supplement for families on low earnings, in a letter from poverty campaigners, faith leaders, academics and charities.

An update from the Scottish Government about the income supplement - due to be introduced in 2022 - is expected on Wednesday.

More than 70 organisations and campaign leaders have signed the letter urging the introduction to be brought forward.

The letter warns "child poverty projections for the coming years are stark", with official Government forecasts predicting the child poverty rate will rise to 35% by 2020-21.

It argues the proposed introduction of the supplement to top up families' incomes in 2022 is "simply too far away".

Describing the measure as a "valuable lifeline", the joint letter calls for four key actions from the Scottish Government - passing legislation for the supplement before the next parliamentary election; putting an interim supplement in place ahead of that; announcing funding for the benefit to be announced in next year's budget, and for the policy to "make substantive progress" towards the Government's poverty targets.

Jackie Brock, chief executive of the charity Children in Scotland, said the early implementation of the family income supplement "would make a crucial difference" to the 240,000 children in poverty across the country.

"The level of poverty many families are experiencing in Scotland in 2019 is an affront to our society's shared instincts about fairness, justice and equality," she said.

"It must not be tolerated. Harsh austerity policies pursued by UK Governments over the last nine years have been the major driving force behind this.

"However, the Scottish Government has the power to act now and stop further increases in child poverty.

"It needs to be bolder and more ambitious if it is to meet its own targets laid out in the Child Poverty (Scotland) Act.

"Early implementation of the family income supplement would make a crucial difference to children and families across Scotland, and would demonstrate that what UN rapporteur on extreme poverty Philip Alston has described as the 'principles of dignity and social security as a human right' are alive in Scotland."

Moderator of the Church of Scotland the Right Rev Colin Sinclair said: "In a caring society we need to ensure that everyone is protected.

"The way we look after our children is a key indicator of how well we are putting our values into practice.

"Delivering the income supplement before 2022 would go a long way to put our words into deeds and would make a significant difference for many families today."

Kerrie Friel, an anti-poverty activist and parent of four, said: "Too many families are being swept up in the rising tide of poverty, struggling to pay bills and put food on the table.

"The new Income Supplement will be a lifeline for families desperate to stay afloat, but we need it now. Kids can't wait."