NEW DELHI—Forty Indian construction workers have been kidnapped from the militant-controlled city of Mosul in northern Iraq, India's foreign ministry said Wednesday.

Ministry spokesman Syed Akbaruddin said it remains unclear who is behind the kidnappings or where the hostages are being held. India is dispatching its former ambassador to Iraq, Suresh Reddy, to the strife-torn nation, the foreign ministry said, and has set up a control room in Delhi to monitor the situation.

Within Iraq, Sunni militants have taken over large swaths of the nation, beating back the country's military in a violent insurgency that threatens to destabilize the region.

Families of several of the kidnapped men say they received phone calls in recent days before the kidnapping. Devender Singh, a 33-year-old laborer who hails from India's northern state of Punjab, phoned his wife this past Sunday and told her "the situation there was scary," a cousin of his said in an interview late Wednesday. The family's two children, five and seven years old, "haven't been informed that their father is in trouble," according to the cousin, Arvinder Singh.

Details remain sketchy and it is too early to draw conclusions about the hostage-taking, said Leela Ponappa, a former deputy national security adviser under the Congress party-led government from 2007 to 2009. So far, she said, there are few suggestions that "Indian nationals are being targeted per se" by kidnappers. She considered it more likely that the workers were "just caught in a serious conflict zone."