The Greek coastguard has caused the deaths of dozens of migrants in the Mediterranean over a three-year period, witnesses say, including nine who were deliberately thrown into the water.

The nine are among more than 40 people alleged to have died as a result of being forced out of Greek territorial waters, or taken back out to sea after reaching Greek islands, BBC analysis has found.

The Greek coastguard told our investigation it strongly rejects all accusations of illegal activities.

We showed footage of 12 people being loaded into a Greek coastguard boat, and then abandoned on a dinghy, to a former senior Greek coastguard officer. When he got up from his chair, and with his mic still on, he said it was "obviously illegal" and "an international crime".

The Greek government has long been accused of forced returns - pushing people back towards Turkey, where they have crossed from, which is illegal under international law.

But this is the first time the BBC has calculated the number of incidents which allege that fatalities occurred as a result of the Greek coastguard's actions.

The 15 incidents we analysed - dated May 2020-23 - resulted in 43 deaths. The initial sources were primarily local media, NGOs and the Turkish coastguard.

Verifying such accounts is extremely difficult - witnesses often disappear, or are too fearful to speak out. But in four of these cases we were able to corroborate accounts by speaking with eye witnesses.

Our research, which features in a new BBC documentary, Dead Calm: Killing in the Med?, suggested a clear pattern.

In five of the incidents, migrants said they were thrown directly into the sea by the Greek authorities. In four of those cases they explained how they had landed on Greek islands but were hunted down. In several other incidents, migrants said they had been put onto inflatable rafts without motors which then deflated, or appeared to have been punctured.

One of the most chilling accounts was given by a Cameroonian man, who says he was hunted by Greek authorities after landing on the island of Samos in September 2021.

Like all the people we interviewed, he said he was planning to register on Greek soil as an asylum seeker.

"We had barely docked, and the police came from behind," he told us. "There were two policemen dressed in black, and three others in civilian clothes. They were masked, you could only see their eyes."

He and two others - another from Cameroon and a man from Ivory Coast - were transferred to a Greek coastguard boat, he said, where events took a terrifying turn.

“They started with the [other] Cameroonian. They threw him in the water. The Ivorian man said: ‘Save me, I don’t want to die… and then eventually only his hand was above water, and his body was below.

"Slowly his hand slipped under, and the water engulfed him."

Our interviewee says his abductors beat him.

"Punches were raining down on my head. It was like they were punching an animal." And then he says they pushed him, too, into the water - without a life jacket. He was able to swim to shore, but the bodies of the other two - Sidy Keita and Didier Martial Kouamou Nana - were recovered on the Turkish coastline.

The survivor’s lawyers are demanding the Greek authorities open a double murder case.