The convicts, sentenced to death for trying to import hashish into the Saudi kingdom, were decapitated by sword in northern and eastern Saudi Arabia on Tuesday.
The Iranian convict was identified as Raza Abbas Fadhil Aderisawi, who was beheaded in the east of the country.
The Syrian nationals, who were executed in the northern region of al-Jawf, were identified as Hamoud Fayez Hassoun, Hassan Taha Musalamani, and Youssef Abdullah al-Halqi.
Tuesday’s executions raise the number of people decapitated by sword in Saudi Arabia over the past four weeks alone to 30.
At least 45 people have been sentenced to death in Saudi Arabia this year. The Saudi regime carries out capital punishments mostly by beheading.
Saudi Arabia, with one of the highest rates of executions in the world, has frequently been criticized by human rights organizations.
“Any execution is appalling, but executions for crimes such as drug smuggling or sorcery that result in no loss of life are particularly egregious,” said Sarah Leah Whitson of Human Rights Watch.
Saudi Arabia, ruled by a hereditary royal system, enjoys full support of its close ally the United States.
In July, UN High Commissioner for Human Rights Navi Pillay censured Saudi Arabia for harassing human rights activists under a failed judicial system.