The family of a Toronto university student who survived a militant attack in Bangladesh says the young man is being held by authorities in the country's capital.

Tahmid Hasib Khan's family on Wednesday called for his release, saying police have not explained why they're detaining the 22-year-old, who is a permanent resident of Canada.

Khan's family says he traveled to Dhaka to visit family. They say he 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 — nine Italians, seven Japanese, an Indian and three students from American universities — were killed in the siege at the upscale restaurant in Dhaka's diplomatic zone.

Authorities held five former hostages for questioning but have released three.