A European Union border agency patrol boat carrying five people, including the Estonian ambassador to Greece, sank off the Greek island of Kastellorizo, according to the Greek coast guard. The incident occurred off Greece’s easternmost island, the coast guard said on Monday, as four of the passengers were injured.

The Frontex patrol boat capsized and sank, the coast guard said, without giving a reason for the sinking. The service said four Estonians and one Greek Frontex liaison officer were on board when the boat went down.

The five people were rescued by a Greek coast guard boat and a passing sailboat, the coast guard said. From there, they were taken to Kastellorizo, where the injured people were prepared for further medical treatment.

The coast guard said four of the rescued passengers were then airlifted to Rhodes for care. The coast guard did not specify whether the Estonian ambassador was among the four people who were injured.

Frontex has long operated in Greece, working alongside Greek maritime authorities as part of the European Union’s border efforts. Greece is one of the main routes into the European Union used by people fleeing conflict and poverty in Africa, the Middle East and Asia, the report said.

The incident follows an earlier Frontex-related accident: last July, a Frontex patrol boat operated by the Portuguese Maritime Police sank off the eastern Aegean island of Lesbos during a search and rescue operation involving a boat carrying migrants. In that earlier case, there were no injuries reported.