Greek authorities are investigating the deaths of three migrants over the past week in a camp on the eastern Aegean Sea island of Lesbos.

Two of the men, an Egyptian and a Syrian national, were found dead in their tents in the Moria camp last week. A third migrant, a Pakistani, died in his tent Monday.

Initial indications suggest they were poisoned by fumes from stoves lit inside the tents to counter bitter winter conditions.

Greece's immigration ministry said Tuesday a coroner's report is pending. A full post-mortem could not be held on Lesbos and samples from the bodies have been sent to Athens.

About 5,000 refugees and other migrants are trapped on Lesbos following Balkan border closures last year and the European Union's deal with Turkey to control immigration.