The Syrian army says rockets have struck several military bases in the Hama and Aleppo countryside in what it says is new "aggression" by its enemies, state television reports.
In a news flash, state television said the missile attacks took place at 10.30pm local time on Sunday.
"Syria is being exposed to a new aggression with some military bases in rural Hama and Aleppo hit with enemy rockets," an army source was quoted as saying without elaborating.
Earlier, state television said successive blasts were heard in rural Hama province and that authorities were investigating the cause.
An opposition source said one of the locations hit was an army base known as Brigade 47 near Hama city, widely known as a recruitment centre for Iranian-backed Shi'ite militias who fight alongside President Bashar al-Assad's forces.
An intelligence source who closely follows Syria said it appeared that multiple missile strikes hit several command centres for Iranian-backed militias and there were dozens of injuries and deaths.
The strikes hit weapons warehouses, and further explosions were heard, the source who requested anonymity said.
Reuters could not verify the authenticity of the allegations.
Israel in the course of the conflict has hit Iranian-backed militia outposts in Syria, targeting mainly Lebanese Shi'ite militia Hezbollah's arms convoys in and out of Syria and its supply lines.
Israeli Prime Minister Benjamin Netanyahu said this month his country will continue "to move against Iran in Syria."
Earlier this month, the New York Times, quoting an unnamed Israeli military source, reported that Israel struck a Syrian air base that Tehran used. Iran's Tansim news agency said seven Iranian personnel were killed in the attack.
The strike on an air base brought warnings from Tehran it would retaliate. Israel has said Iran was expanding its influence in a belt of territory that stretches from the Iraqi border to the Lebanese border, where Israel says Iran supplies Hezbollah with arms.
Hezbollah and other Iranian-backed militias have a large military presence in Syria and are well entrenched in central and eastern areas near the Iraqi border.