The Islamic State militant group executed 18 Syrian soldiers in the country's ancient city of Palmyra, reported a monitor group on Monday.

The IS informed the locals of Palmyra that they were going to be executed for being part of the "infidel army" of the Syrian regime, according to the Syrian Observatory for Human Rights. These soldiers were captured during their battles against the IS militants in Palmyra.

The Britain-based watchdog group reported that the executions took place in a public square in Palmyra, stopping short of providing further details concerning the date.

In July 2014, IS released a video footage of the execution of 25 Syrian soldiers in Palmyra.

IS seized full control of Palmyra, also known as Tadmur, this May.

Since then, IS has destroyed the city's notorious military prison as well as several Islamic tombs.

IS also publicly executed individuals suspected of working for the government.

Their most recent victim was Khaled Asaad, a prominent Syrian archaeologist and a Palmyra resident for most of his life, who was dedicated to his career of studying Palmyra's archaeological sites.

Government officials said IS militants attempted to extract information from Asaad regarding Palmyra's "hidden gold," which, according to them, is a myth.

Palmyra is known for its monumental ruins, the remains of a great city which was once one of the ancient world's most important cultural centers.

Syria includes prehistoric Greek, Byzantine and Islamic archeological remains.

Before the crisis, Syria used to attract countless multinational archaeological missions, searching for historical threads in their efforts to decipher the evolution of ancient civilizations.