A petition by separatists in the Canadian province of Alberta was formally filed by its organisers on Monday, marking a key step towards a possible independence referendum in the autumn.

Stay Free Alberta, the group behind the citizen-led petition, has said that it has surpassed the amount of signatures needed to trigger a referendum.

The Alberta separatist movement has its roots in what is known as western alienation - a term used to describe the belief by some that the province is often overlooked by decision-makers in the national capital, Ottawa.

Petition organisers had until this month to collect at least 178,000 signatures - or 10% of eligible voters - for the referendum campaign.

Mitch Sylvestre, the head of Stay Free Alberta, said outside the election office in Edmonton on Monday that the organisation delivered more than 300,000 signatures.

"This day is historic in Alberta history," he said. "It's the first step to the next step - we've gotten by Round 3 and now we're in the Stanley Cup final."

However, verification of signatures has been paused by an Alberta court pending a decision on a legal challenge by a group of indigenous First Nations, who argue the push to separate from Canada infringes on their rights.

A decision in the case is expected to come later this month.

Kevin Hille, lawyer for the Athabasca Chipewyan First Nation, said he thinks his clients have a good case that may shut down the referendum question.

"An international border would impact their treaty rights and way of life," Hille told the BBC, referencing treaty agreements forged between the British Crown and First Nations communities more than a century ago, before the creation of modern-day Canada.

He added that his clients believe an independent Alberta would mean the severing of those treaties.

Hille noted a separate decision made by an Alberta court in December, in which a judge ruled that an independence referendum would be unlawful because it violates First Nations' rights as set out by Canada's constitution.

The Alberta government, however, has allowed the petition process to continue after amending its laws to remove a requirement for citizen-initiated referendums to be constitutional.

The latest case before the courts asks if the December decision holds despite that change, Hille said.

If successful, Hille said an independence referendum would not be allowed to go ahead unless it is proposed by the provincial government.

If petition signatures are ratified, Albertans could vote in an independence referendum as early as 19 October.

The question would ask: "Do you agree that the Province of Alberta should cease to be part of Canada to become an independent state?"

Anger with Ottawa has long been brewing in the western province, in particular over development of its natural resources, with some Albertans believing that federal government, especially under the Liberals, has stood in the way of the province's oil and gas industry in favour of pro-climate legislation.

Previously on the political fringes, the possibility of a unity crisis has become increasingly likely in the last year.

Still, polls suggest that the majority of Albertans would vote against separating from Canada, with about 25% being in favour, according to a February survey by Canadian polling firm Abacus Data.

A counter "Forever Canadian" citizen-led petition launched in opposition to separation received 450,000 signatures, and is currently in front of a committee that will determine its future.

Proponents of separation believe that an independent Alberta would unlock resources while retaining the province's wealth.

Members of the movement have also met with officials from the Trump administration.

Jeff Rath, one of the organisers and a lawyer advocating for Alberta independence, told the BBC in January that the meetings were to discuss "a feasibility study" on a possible $500bn (£362bn) line of credit should the province separate, he said, adding that his group was not soliciting funding from the US. (BBC)

Update news