Two Dutch teenagers found dead in their hotel room in Istanbul last August were killed by the insecticide phosphine gas, not food poisoning as thought earlier, Turkish media have reported.

The brothers, aged 15 and 17, were staying at the hotel with their father. Hotel staff found their bodies when they went into the room after the family failed to check out. Their father was taken to hospital in a critical condition but has since recovered.

The new cause of death comes from the toxicology report on the brothers. It was made public at the start of a trial of six hotel staff and pest control workers who have been charged with causing the deaths of a family of four from Germany.

They  were also poisoned by insecticide in a separate incident while staying at a different hotel.

Turkish media say five people have been arrested in connection with the death of the Dutch brothers, including hotel staff and the head of the pest control company brought in by the hotel.