The family of a Toronto student who was detained after surviving a bloody hostage-taking in Bangladesh said Monday that they haven't been able to contact him for a week and are concerned about his well-being.

Tahmid Hasib Khan, a 22-year-old permanent resident of Canada, has been in custody in Dhaka ever since the July 1 attack. The family doesn't know why he's being held, but they insist Khan is innocent.

"The more days go by, the more we're getting concerned because Bangladesh police and army, they don't have a very good human rights record," said Khan's older brother, Talha Khan, who is in Toronto.

Talha Khan said his brother traveled to Dhaka to celebrate Eid with family and was meeting friends at a Dhaka café when he and others were taken hostage for 10 hours on July 1.

Two police officers and 20 hostages were killed in the siege at the upscale restaurant in Dhaka's diplomatic zone. Six of the attackers also died.

Tahmid Khan, an undergraduate student studying global health at the University of Toronto, had plans to go on to Nepal where he was to begin an internship this week but he was detained after the attack ended. His family fears authorities may suspect him of being linked to the attackers, who have been identified as coming from well-off families.

"We want to know why he is being held, as a witness, or as a suspect," said Khan's brother, who is a Canadian citizen. "He was just in the wrong place at the wrong time. Nothing in his life points towards any sort of extremism."

Khan's father was able to speak with his son twice in the early days of his detention, but the family has not been able to reach him for a week.

"We know he is in Dhaka but where exactly we don't know," Talha Khan said.

The family has reached out to Canada's Foreign Affairs Minister Stephane Dion through a Canadian lawyer, but has not heard back.

Global Affairs Canada said it was monitoring the situation in Bangladesh closely. A spokeswoman added that "there are limits" to what any country can do for individuals who are not its citizens.

The entire situation has taken a tremendous toll on the parents, his brother said, noting that his mother has suffered an emotional breakdown and his father was hospitalized on Monday after a suspected heart attack.

"We understand that it's a national security issue, but at least if my parents could go and see him, that would be some kind of solace," said Talha Khan. "At least communication to begin with."