IT ALL started with a single tweet.

Last Friday, Canada said it was “gravely concerned” by the arrest of women’s rights campaigners in Saudi Arabia, including award-winning activist Samar Badawi.

Since then, relations between the two countries have only plunged further and further.

First, the Middle Eastern giant expelled the Canadian ambassador from Riyadh and recalled his Saudi counterpart in Ottawa.

Then it suspended all Saudi state airline flights to Toronto, ended thousands of scholarship programs for Saudi students in Canada, and froze “all new business” with Ottawa.

Now, Saudi authorities have announced they will halt all medical treatments in Canada, and transfer Saudi patients to hospitals outside the country.

They’ve also moved to withdraw 800 Saudi medical students working around the country.

It’s yet another warning to the West reflecting Riyadh’s newly assertive foreign policy.

Asked if the Canadian government would consider apologising, Prime Minister Justin Trudeau told journalists: “Canadians have always expected our government to speak strongly, firmly, clearly and politely about the need to respect human rights at home and around the world. We will continue to do that.”

Meanwhile in Riyadh, Saudi Arabian Foreign Minister Adel al-Jubeir told reporters Canada needed to “fix its big mistake”.

“There is nothing to mediate. A mistake has been made and a mistake should be corrected,” he said. “The ball is in Canada’s court.”

He also noted the kingdom was considering taking “additional measures” against Canada, without going into detail.

CANADA THREATENED IN 9/11-STYLE TWEET

Earlier in the week, a now-deleted tweet from a Saudi Arabian non-profit group was accused of supporting a 9/11-style attack on Canada.

“Sticking one’s nose where it doesn’t belong! As the Arabic saying goes: He who interferes with what doesn’t concern him finds what doesn’t please him,” the tweet said.

It then showed a plane flying towards the Toronto skyscrapers, which drew comparisons on social media to the September 11 attacks in New York, where 15 of the attackers were Saudi citizens.

The tweet was quickly deleted, but now the Saudi government has gotten involved.

In a tweet from the Saudi media account it states: “Based on a complaint filed to the Ministry of Media about a post by @Infographic_ksa, the ministry has ordered the owner of the account to shut it down until investigations are completed, according to electronic broadcasting laws in KSA.”

And Fatimah Baeshen, the spokeswoman for the Saudi embassy in the US said she was “horrified”.

“Totally unacceptable, regardless of the intent. Glad these kids apologised and clarified what they meant,” she tweeted.

The Twitter account behind the original tweet said the image was meant to symbolise the Canadian ambassador flying back to Canada.

WHAT’S SAUDI ARABIA PLAYING AT?

Analysts say Saudi Arabia is using Canada to send a message to the world: don’t criticise our kingdom or our human rights record.

It reflects Riyadh’s newly assertive foreign policy under Prince Mohammed bin Salman Al-Saud.

“It’s pretty clear that he’s using Canada to send a message to the rest of the world that if you want to trade with Saudi Arabia, then you need to shut up on human rights,” Nader Hashemi, director of the University of Denver’s Center for Middle East Studies at the Josef Korbel School of International Studies, told Al Jazeera.

He said the prince is “drunk on power”, “arrogant” and “believes that he has Donald Trump in his back pocket and can do whatever he wants”.

The United States, which has strong ties with both Saudi Arabia and Canada, has taken a neutral stance in the feud.

“Both sides need to diplomatically resolve this together,” State Department spokeswoman Heather Nauert told reporters. “We can’t do it for them. They need to resolve it together.”

President Donald Trump has been reluctant to criticise Saudi Arabia for its human rights record, and escapes focused criticism from the State Department.

— With wires