While the state-owned daily Tishreen said the missiles were launched from U.S. and British military bases, analysts said the most likely source was Israel, which has previously acknowledged carrying out more than 100 strikes in Syria during the civil war.
The Britain-based Syrian Observatory for Human Rights said Israel carried out the attacks. The monitoring group identified the main target as an arms depot for surface-to-surface missiles at a base in northern Syria known as Brigade 47. It said the Neirab military air base, southeast of Aleppo city, also was hit.
At least 26 people were killed, four of them Syrians, the Syrian Observatory said. Representatives of a regional alliance that includes Iran, Syria and the Hezbollah paramilitary group said that Iranians were among the dead, and some cited a much higher toll.
The names and faces of some of the dead appeared to be circulated across loyalist websites all day Monday with captions describing them as heroes and victims of “wanton aggression.”
In Iran, there were conflicting reports on the casualties and on whether Iranian assets were struck. Tehran has sent thousands of fighters to bolster Syrian President Bashar al-Assad, including proxy forces from Iraq and Afghanistan.
Seven years after Syria’s largely peaceful uprising morphed into a civil war, the country is now the stage for proxy conflicts of global powers.
Israel has watched anxiously as Iran shored up Assad’s rule with weapons and money, then committed its own troops and developed military infrastructure across the country.
Israel has been pushing for the United States to maintain a military presence in Syria to counterbalance Iran. U.S. forces already have clashed with Iranian-backed militias that had advanced against positions of local fighters supported by the United States.
Israel has escalated its warnings about Iran in recent weeks, as a U.S. deadline approaches for deciding whether to remain in the 2015 Iran nuclear deal. Israel’s leadership is pushing for the deal to be scrapped or adjusted, although some in the security establishment have warned of the instability that may cause.
The Lebanese newspaper al-Akhbar, which supports the Syrian government, reported that the targets struck Sunday night were weapons storage sites for the regime and Iran’s Revolutionary Guard Corps. The newspaper said that “bunker-buster” bombs were used.
Iran has threatened to retaliate against Israel following the death of seven of its officers in an Israeli strike on the T-4 military base in Syria in early April.
Speaking in Washington on Sunday, Israeli Defense Minister Avigdor Liberman said Israel had three problems: “Iran, Iran, Iran.”
He has threatened to hit back if Iran retaliates for the T-4 attack.
Jonathan Spyer, a fellow with the Jerusalem Institute for Strategic Studies, said it appeared to be “common sense” that Israel was responsible for Sunday night’s strikes.
Spyer said that with Israel determined to prevent the “consolidation and entrenchment” of Iranian influence in Syria, “the chances of confrontation between Israel and Iran are quite significant.”
Speaking to reporters in Jerusalem, Michael Oren, a deputy minister in the prime minister’s office and a former ambassador to the United States, declined to directly comment on the strikes but said Israel is committed to enforcing its “red lines.”
“If that leads to an escalation, it is on the heads of Syria,” he said.
Morris reported from Jerusalem. Suzan Haidamous in Beirut contributed to this report.