ATHENS (Reuters) - Greek coastguard officers will testify as suspects as part of a disciplinary investigation into their role in a deadly migrant shipwreck off Greece, three sources told Reuters on Thursday.

Hundreds are feared to have died when a vessel, monitored by the Greek coastguard for several hours, capsized and sank in international waters off the southwestern Greek coastal town of Pylos on June 14, 2023.

Up to 700 people were in the trawler which left Libya heading for Italy. Some 104 survivors were rescued but only 82 bodies were recovered. One year on, no one has been held accountable and relatives are still waiting for news of loved ones.

The Greek coastguard has denied any wrongdoing over the handling of the case that sent shockwaves across Europe and beyond and raised questions about the European Union's tactics on migration.

About 10 officers, including the coastguard's commander and the captain of the vessel monitoring the overcrowded ship before it sank, have been called to testify as suspects, the sources who are close to the inquiry said.

The officers will be questioned as part of an investigation launched by Greece's ombudsman Andreas Pottakis - who has the authority to investigate the actions of security forces on a disciplinary level and is examining whether coastguard actions or omissions helped cause the tragedy.

The cause of the shipwreck is still disputed. Survivors say the coastguard caused the boat to capsize when it tried to tow it. The coastguard has said that the boat refused assistance.

"Adequate indications" of wrongdoing throughout the search and rescue operation have emerged, one of the sources said.

The suspects will testify over gaps in the coastguard's communications' log and whether a rescue operation was properly planned, the sources said.

Other questions will look into whether the vessel that arrived at the scene to shadow the migrants' trawler was adequately equipped for a rescue mission and whether, and if so why, there were special forces on board.

If the investigation concludes that officers involved in the operation were accountable at any stage, they will be called to respond to the accusations. They could face disciplinary action, with the highest penalty being dismissal from the service.

A naval court, the only judicial body in Greece that can examine any criminal responsibility of coast guard officers opened a separate investigation last year, but it is still at a preliminary stage.

(Additional reporting by Yannis Souliotis; Editing by Hani Richter and Andrew Heavens)

By Renee Maltezou