The militants also broke up a hidden 2,000-year-old lion statue they had discovered in a Palmyra museum garden and demolished a 13th-century tomb near the northern Iraqi city of Kirkuk.
The destruction, publicized in photographs and statements posted by the Islamic State on social media and corroborated by officials and antiquities experts, underscored the risks to the archaeological heritage sites in Syria and Iraq, as well as the impunity of the militants in command of large parts of both countries.
On Thursday, the Islamic State, also known as ISIS, said it had smashed at least six statues from Palmyra seized from a smuggler in an area of Aleppo controlled by the group's operatives in northern Syria.
It said the smuggler had been prosecuted by a Shariah court in the town of Manbij and punished with a public flogging. Photos posted by the Islamic State included a sledgehammer and statue remnants.
On Friday, Iraqi antiquities experts said the Islamic State had wrecked a tomb dating from the middle of the 13th century about 7 miles west of Hawija, in Kirkuk province. Before-and-after photographs showed the rubble.
"This is a terrible and tragic addition to ISIS' long list of never-ending and incomprehensible destruction of some of Iraq's and Syria's most important historic monuments," said Ihsan Fethi, a heritage expert and member of the Iraqi Architects Society.
Dismissing international outrage over its pillaging of ancient treasures in the two countries, the Islamic State has said it regards artifacts as sacrilegious vestiges that deserve to be obliterated. In propaganda videos and photos, the group has detailed the wreckage of a museum in Mosul, Iraq, and important archaeological sites in Nimrud, Hatra and Nineveh, Iraq.
On Thursday, Irina Bokova, director general of UNESCO, the U.N. Educational, Scientific and Cultural Organization, who has been outspoken in her denunciations of the Islamic State, told a meeting in London that the antiquities destruction had "reached unprecedented levels in modern history."
In May, as Islamic State fighters encircled Palmyra in central Syria, antiquities officials there rushed to move or hide many of the city's treasures. The city is known for its 2,000-year-old ruins.
Last month, the group blew up two historic tombs near Palmyra, online photographs showed. But Thursday was the first time that the Islamic State said it had destroyed Palmyra statues.
There also was speculation that Islamic State fighters might have posted photographs of fake statue remnants and sought to smuggle the real ones themselves.
The Syrian Observatory for Human Rights, a British-based group with a network of monitors inside Syria, said its sources in Manbij, where the purported statue smuggler was punished, said the Islamic State had confiscated the statues "in preparation to sell them in one of the neighboring countries." The observatory's account could not be corroborated.
Syria's official news agency, which said at least eight plundered Palmyra statues had been confiscated by the Islamic State in Manbij, also reported the destruction of a famed 2,000-year-old statue in Palmyra on Thursday. Known as Allat God, the statue depicts a lion catching a deer between its paws.
The agency said that the statue, discovered in 1977, had been hidden inside an iron box in a Palmyra museum garden for protection but militants had discovered the hideaway and broken Allat God into pieces.
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