The Prime Minister’s Office is calling for the immediate release of two Canadians who have been held in a notorious Egyptian jail, without charges, for six weeks.

In a statement released to CTV News on Sunday, the PMO said: “In the absence of charges, Dr. Loubani and Mr. Greyson should be released immediately."

It’s the strongest language to date from the PMO.

The statement came hours after Egyptian prosecutors announced that John Greyson and Dr. Tarek Loubani would remain in Cairo's Tora prison for another 45 days.

Greyson and Loubani were arrested on Aug. 16, amidst violent clashes between supporters of ousted president Mohammed Morsi and Egyptian security forces.

On Sept. 16, both men began a hunger strike to protest the arbitrary nature of their detention.

Foreign Affairs Minister John Baird said he met with his Egyptian counterpart on Friday, to "raise the case of Dr. Loubani and Mr. Greyson."

"I appreciated the high-level engagement but impressed upon them the importance of file to the Government of Canada," Baird said in a series of tweets Saturday.

Greyson's sister, Cecilia Greyson, said Sunday she was "disappointed" that the pair’s detention has been prolonged.

"To have the detainment extended for another 45 days is truly awful for all of us," Cecilia told CTV News Channel.

Asked about the possible reasons behind Loubani and Greyson's ongoing detention, Cecilia said she believes the Egyptian government has "political motivations" for keeping the pair imprisoned given the fact, she says, that "John and Tarek witnessed the deaths of over 50 Egyptians" on Aug. 16.

"They aren't following any kind of legal protocol that we can recognize. They refuse to look at our documentation that we've provided," she said. "There are simply no charges that could ever be laid against John and Tarek that would hold validity in court."

Egyptian prosecutors have accused Loubani and Greyson of "participating with members of the Muslim Brotherhood" in an attack on a police station, but the pair and their supporters insist they were just passing through on their way to Gaza.

Greyson's sister says lawyers working for the jailed Canadians told her the extension applies to everyone who was arrested during protests in the Egyptian capital that day.

She said the pair's lawyers have launched an appeal to free the men and a decision from Egyptian prosecutors could come within days.

On Saturday, a statement from the two men was made public.

In the letter, which was dictated by the pair to their lawyers and later relayed to family members, Loubani and Greyson describe the "ridiculous conditions" of their detention and call on authorities to set them free.

"We deserve due process, not cockroaches on concrete. We demand to be released."

Under Egyptian emergency law, CTV News has learned the pair can be detained in prison for up to two years without charges.

Cecilia said she has not had any direct communication with her brother or Loubani, but she has been able to send "little messages" through the pair's lawyers.

With a report by CTV's Richard Madan in Ottawa