The militant group said on its Dabiq news agency that it had targeted "an individual of the apostate Syrian regime" in the city of Mayadin in Deir al-Zor province using a pistol, and attacked two other personnel with machine guns in the northern city of Raqqa.
Syria's Defence Ministry said in a statement that a Syrian army soldier and a civilian were killed on Saturday by "unknown assailants".
A military source told Reuters the soldier belonged to the army's 42nd Division.
The attacks come amid a sharp escalation by IS against Syria's leadership under President Ahmed al-Sharaa, a former al-Qaeda leader who broke with the group in 2016 before leading a coalition of Islamist factions that overthrew President Bashar al-Assad at the end of 2024.
On Saturday evening, IS released a recorded statement by its spokesperson, Abu Hudhayfa al-Ansari, who said Syria had "moved from Iranian occupation to Turkish-American occupation."
The group said it had begun a "new phase of operations" in Syria, describing Sharaa as a "watchdog" of the global coalition and vowing that his fate would be no different from that of Assad.
Sharaa signed Syria's accession to the global coalition to defeat IS during a visit to the US in November, when he met President Donald Trump.
The latest incidents come two days after IS claimed responsibility for another attack in Deir al-Zor that killed a member of the Interior Ministry's internal security forces and wounded another.
Several social media accounts and Telegram channels supporting IS have in recent hours called for intensified attacks using motorcycles and firearms.
IS has carried out six attacks against Syrian government targets since the fall of Assad.
A report by the UN Office of Counter-Terrorism released last week said Sharaa and two senior cabinet ministers had been targeted in five foiled assassination attempts by IS.
