Ottawa has not been told why two Canadians have been detained in Egypt, and Prime Minister Stephen Harper says the government is "extremely concerned" about their safety.

Word got back to Canada on Friday that John Greyson, a Toronto-based filmmaker and York University professor, and Tarek Loubani, an emergency room doctor from London, Ont., had been detained in Cairo.

Greyson and Loubani had planned to head to Gaza, but the border was closed when they landed in Cairo the day before their arrest. That led to an unplanned stay in the city where they were detained.

Loubani was going to Gaza to train emergency room doctors. Greyson was accompanying him, hoping to make a documentary.

Their detention comes amid bloody clashes between Egyptian security forces and supporters of ousted prime minister Mohammed Morsi that have claimed almost 1,000 lives in recent days.

Canadian consular officials visited Greyson and Loubani on Sunday, and passed a message on to their loved ones the two men are OK.

What is not clear is why the Canadians have been detained.

"We are obviously extremely concerned about the arrest and treatment of the two Canadian citizens who have been detained in Egypt," Harper said Monday during a news conference in Whitehorse, Yukon.

"We don't frankly know what evidence supports any such arrest," the prime minister said, "and we have expressed our concerns directly to the Egyptian government."

Those concerns are also weighing on the families of the two men, who want to see Greyson and Loubani moved out of the violence-torn counrty.

A Toronto man was shot dead during a protest in Alexandria, a city located about two hours from Cairo, on the same day Greyson and Loubani were arrested.

Cecilia Greyson, the sister of the detained filmmaker, said the situation has left their family anxiously waiting for information.

"We’re all very, very worried and we all want to see this resolved as quickly as possible," she told CBC Radio’s Mainstreet in a telephone interview from Halifax.

On Monday, Lynne Yelich, the junior foreign affairs minister, released a statement saying the government was trying to obtain more information about why the men had been detained.

But Yelich said the government strongly believes "this is a case of two people being in the wrong place at the wrong time."

Yelich vowed that Canada will continue to press for a timely resolution on the case. 

Deepak Obhrai, parliamentary secretary to Foreign Affairs Minister John Baird, said in an interview on CBC News Network that steps are being taken to get more information.

"We are calling the Egyptian ambassador for the second time and we will be writing a letter to the Ministry of Foreign Affairs of Egypt," Obhrai said.

"But what we really want — if they are being held for real reasons — we want to see the charges, what the charges are … If not, then they should be released."

Clashes began last Wednesday between security forces and supporters of the Muslim Brotherhood. Supporters are seeking the reinstatement of Morsi, toppled by the army on July 3 after mass demonstrations against him.

Officials in Ottawa are warning Canadians to avoid any non-essential travel to Egypt.

With files from the CBC's Michelle Cheung and The Canadian Press