The Islamic State (Isis) group threw a man off a building and subsequently had him stoned to death by a mob of onlookers in the last of a series of similar killings targeting homosexuals in Syria.

Jihadists are seen pushing a blindfolded man off a rooftop in the al-Tabqah area, in the northern Raqqa province, in disturbing images posted online.

The young victim is finished off by a crowd of residents who had gathered outside the building to witness the execution.

The brutal murder was carried out at the end of February, activist groups said.

Local opposition collective Raqqa is Being Slaughtered Silently, which documents IS human rights abuses, said the man in his 20s had been accused of "being gay".

The execution was confirmed also by the London-based Syrian Observatory of Human Rights (SOHR), which added that a second man was killed "for the same charge and by the same way" a day later in Raqqa, IS de facto capital.

It was not the first time IS advertised such murders online. The Islamist group violently enforces a radical interpretation of Sharia law over the territories it controllers and routinely slays people for sodomy.

Images of men being thrown off buildings and then stoned in several Syrian cities have been published online with horrifying regularity by IS media branch in recent months.