Three candidates -- two women and a Muslim man -- will battle it out to replace Scotland First Minister Nicola Sturgeon, it was announced Friday, in a race already mired in controversy.

Kate Forbes, Ash Regan and Humza Yousaf all met the threshold of support needed to enter the contest to replace the long-serving Scottish National Party (SNP) chief following her shock resignation, the party announced.

The announcement came amid an uproar over Forbes' conservative views on gay marriage.

The finance secretary, a 32-year-old rising star, caused controversy by saying she would have voted against same-sex marriage had she been a member of the Scottish Parliament when the reform passed in 2014.

Forbes is a devout Christian and member of the Free Church of Scotland, Scotland's second largest denomination, which opposes same-sex marriage and abortion.

While Forbes has defended her stance on the issues as a matter of personal conscience, it puts her strongly out of line with the SNP's centre-left base, and four high-profile supporters immediately withdrew their backing.

Despite backlash on social media, Forbes insisted her campaign was "absolutely not over" so soon after it began.

"We have a large party membership, most of whom are not on Twitter," she told BBC radio.

"My position on these matters is that I will defend to the hilt everybody's rights in a pluralistic and tolerant society, to live and to love free of harassment and fear."

Forbes, who has been on maternity leave after having a baby in August, also explained her religious disapproval of pre-marital sex.

"In terms of my faith, my faith would say that sex is for marriage and that's the approach that I would practise," she told Sky News.

Despite the furore, a Big Partnership poll of 1,001 Scots who voted SNP in 2021, released on Friday, put Forbes slightly ahead of her competitors on 28 percent, although 31 percent said they were still undecided.

Surprise resignation

The controversy around Forbes came as a boost to the rival leadership campaign of Health and Social Care Secretary Humza Yousaf, 37.

Yousaf, who is Muslim and backed by allies of Sturgeon, told the BBC that he would "always fight for the equal rights of others" and would not legislate based on his own faith.

Regan has stated her opposition to a controversial measure pushed through by Sturgeon allowing people to change gender without a medical diagnosis, from the age of 16.

All three candidates have vowed to reinvigorate Sturgeon's spluttering push to win independence for Scotland, after the UK government blocked her plans to hold a fresh referendum on the issue.

Forbes has polled well in Scotland since taking over the finance role and presenting a budget at the last minute in 2020, when her predecessor quit after sending an inappropriate message to a 16-year-old boy.

Yousaf has his own political problems from mounting issues in Scottish healthcare under his watch, and from contentious hate crimes legislation he pushed in a previous portfolio.

The leadership race was ignited when Sturgeon last week announced her surprise resignation, after more than eight years as Scotland's first minister and SNP chief.

It is the SNP's first full leadership battle since 2004, as Sturgeon was elected unopposed in 2014. Nominations closed on Friday at noon with the ballot opening at noon on 13 March 2023.

The new leader is set to be announced on March 27.