The agreement between the Scottish National Party (SNP) and the Scottish Green Party needs to be approved by members but tightens ties between the two parties, which both back a new vote on independence.

The deal promises to deliver another referendum before the end of the first half of the current parliamentary session in 2024, if the coronavirus crisis had ended.

First Minister and SNP leader Nicola Sturgeon hopes to secure the so-called "indyref2", despite strong opposition from the UK government in London.

"For my part, I am determined there will be an independence referendum in this parliament," she said at a joint press conference at her Edinburgh residence, Bute House.

"We (the SNP and the Scottish Green Party) are choosing to work together and we are doing so not out of necessity but for the common good.

"We also in this agreement reaffirm our shared commitment to securing independence."

The deal is not a coalition, however, according to its text. The Greens will get two ministerial positions. Appointments have yet to be announced.

Greens co-leader Patrick Harvie hailed the agreement as a "historic moment" but insisted the two parties would retain their "distinctive voices".

Party members have to vote next week on whether to back the deal.

It comes as the UK government prepares to host the COP26 UN climate change summit in Glasgow, western Scotland, from November 1.

Campaigners, including Friends of the Earth Scotland, said they hoped the alliance would help prioritise environmental issues to combat global warming.

The Scottish Greens have just eight seats in the 129-seat parliament in Edinburgh, which has powers to set policy in areas such as health, education, transport and the environment.

The SNP, which has been banking on Scottish opposition to the UK departure from the European Union, has 64, just short of an overall majority.

The last independence referendum in Scotland in 2014 saw 55 percent vote against severing ties with England, Wales and Northern Ireland.