Al-Qaeda's Syrian branch on Wednesday executed a man it accused of insulting the Prophet Mohammed, in a summary killing mirroring those by the Islamic State group, a monitoring group said.
Al-Nusra Front militants shot dead the civilian, identified as Mohammad al-Mir, in the town of Irbin, just northeast of the capital Damascus, said the Syrian Observatory for Human Rights.
The man had been accused of "insulting the Prophet Mohammed and his family," said the Britain-based monitoring group.
Al-Nusra has regularly executed members of Syrian President Bashar al-Assad's regime, but has rarely been accused of carrying out such killings on religious grounds.
It pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri in April, distancing itself from the Sunni extremist Islamic State (IS) group notorious for summarily executing those it accuses of apostasy.
"We are all used to seeing the Islamic State group doing this, but now it seems that other groups like Al-Nusra Front are following in their footsteps, and are terrorising the population," Observatory director Rami Abdel Rahman told AFP.
In December 2013, IS jihadists executed a Syrian boy accused of blasphemy, sparking protests in the northern city of Aleppo and condemnation from activists and Assad's opponents.
The group has since gained infamy for its near-daily executions -- often beheadings -- in areas that it co-opted, and for publicly committing some of the worst atrocities in Syria's war.
Until recently, many Syrian activists and rebels seeking Assad's overthrow had considered Al-Nusra Front to be less radical than the IS group.
In many areas of the war-torn country, Al-Nusra Front members and rebel fighters have fought side by side against forces loyal to Assad.
But in recent weeks, particularly after the launch of US-led strikes against jihadist positions in Syria in late September, Al-Nusra Front has started mobilising to expel rivals from areas out of government control.
Less than a month ago, Al-Nusra pushed out Syrian rebels from most of their positions in the northwestern province of Idlib.
"The killing in Irbin shows us what Al-Nusra Front is really about," said the Observatory's Abdel Rahman.
"The execution violates not only human rights, but also proves once again that Al-Nusra's agenda has absolutely nothing to do with the Syrian people's desire for democracy," he added.
Syria's war began as a peaceful movement demanding Assad's ouster, but later evolved into a war after the regime unleashed a massive crackdown against dissent.
Al-Nusra released its first statement in January 2012, and has since claimed responsibility for the majority of suicide attacks that have struck the country in the past three years.
The group has been classed by the United States since 2012 as a "terrorist" organisation.