The Syrian Observatory for Human Rights said nine children were among the 23 shot dead by IS militants yesterday near the UNESCO world heritage site.
"The Islamic State group executed by gunfire 23 civilians, including nine children, in the village of Amiriyeh, north of Tadmor," Observatory chief Rami Abdel Rahman told AFP.
Palmyra, which means City of Palms, is known in Arabic as Tadmor, or City of Dates.
Abdel Rahman said family members of government employees were among those murdered.
"It is our responsibility to alert the (UN) Security Council so that it will take strong decisions" to protect the famed 2,000-year-old desert oasis site featuring Roman colonnades and an impressive necropolis, she said in Lebanon.
IS would see such cultural treasures as targets, after the group was filmed destroying the Iraqi archaeological sites of Nimrud and Hatra.
Bokova said it was important to work "against extremism, against this strategy of eradicating... Our collective memory", referring to IS destruction of archaeological treasures in Iraq and Syria.
Syria's army sent reinforcements to Palmyra on Friday.
"The army is bombing the surroundings of Tadmor from the air," said Abdel Rahman. "Islamic State group jihadists are now one kilometre" from the ruins.
Since the IS offensive began early Wednesday, more than 138 combatants -- 73 soldiers and 65 jihadists -- have been killed.
Before the latest killings, there were reports of at least 26 civilians executed by IS, including 10 by beheading, for allegedly collaborating with the regime, the Observatory said.
