The bodies of two migrants have been found in the Danube River, near the village of Archar, northwestern Bulgaria, police say.

Most of the Bulgarian section of the Danube serves as a natural border with Romania.

Authorities are now looking for "two boys, two girls and a man" who reportedly also drowned while trying to cross into Romania.

Four foreign nationals have been detained following an alert from locals in the area who spotted them on the island of Dobrina, not far off the mainland, Dimitar Chorbadzhiev, who heads the local border police department, quotes Focus News Agency as saying.

The foreign nationals, supposedly from Iraq despite not having documents, have given indications there are more bodies in the Danube waters.

Speaking to the Bulgarian National Television, a police official has quoted the migrants as saying they had paid in order to be taken to Romania by boat. They headed to the other Danubian bank in two boats, but one capsized.

The incident is reported to have taken place on September 08.

Bulgaria's Interior Minister Rumyana Bachvarova has made clear police is working to detain the suspected smugglers. She has refused to elaborate as "the investigation is ongoing."

Bachvarova has made clear her institution had chosen to make the information public a bit later as the probe required "much more complicated work" than usual.