Hakan Tosun, 50, was found unconscious after being attacked as he walked through the streets of Istanbul's Esenyurt district in the early hours of Saturday morning, a police statement said.

CCTV footage published by Turkish media showed him being attacked by two people, with police confirming they had arrested two men, aged 18 and 24, over the assault.

Tosun was rushed to hospital but died of his injuries on Monday.

He was known for his coverage and documentary work focusing on the struggle to protect the environment, urban activism and the fight against gentrification.

Turkey's Association of Progressive Journalists said attacks on journalists had "become commonplace" in Turkey and demanded "clarity and accountability" about the incident, in a demand echoed by Reporters without Borders (RSF).

"All details about the motive for the attack on his life must be revealed. We are deeply saddened. We demand the harshest punishment for all those responsible," RSF's Turkey representative Erol Onderoglu said.

Environmental groups also issued a statement demanding to know "what happened to Hakan Tosun" with politicians also calling for a full investigation.

"This unacceptable and despicable attack not only targeted a journalist, but also the truth, press freedom, and the right to information," said Burhanettin Bulut, deputy head of the main opposition CHP party.

And the pro-Kurdish DEM party said probing his death was crucial for protecting press freedom.

"Hakan Tosun was a journalist in search of truth and a defender of nature and life. Clarifying all aspects of this suspicious death is essential for press freedom and respect for the right to life," it said on X.