The Israeli military on Thursday said it attacked "dozens" of Iranian targets in neighboring Syria in response to an Iranian rocket barrage on Israeli positions in the Golan Heights, in the most serious military confrontation between the two bitter enemies to date.

Israel said the targets included weapons storage, logistics sites and intelligence centers used by elite Iranian forces in Syria. It also said it destroyed several Syrian air-defense systems after coming under heavy fire. It said none of its warplanes was hit.

The blistering Israeli assault was by far the most intensive Israeli action in neighboring Syria since the civil war broke out there in 2011. Israel has largely tried to stay on the sidelines, but has previously acknowledged carrying out over 100 airstrikes over the past seven years, most believed to be aimed at Iranian weapons shipments bound for the Hezbollah militant group.

There was no immediate word on Iranian casualties. Syria's capital of Damascus shook with sounds of explosions just before dawn, and firing by Syrian air defenses over the city was heard throughout the night.

Syria's state news agency SANA quoted a Syrian military official as saying Israeli missiles hit air defense positions, radar stations and a weapons warehouse, but claiming most incoming rockets were intercepted.

In recent months, Israel has warned that it will not accept a permanent Iranian military presence in Syria. Iran has accused Israel of carrying out a series of deadly strikes on Iranian military positions in Syria in recent weeks, and had vowed retaliation. Iran has sent thousands of troops to back Syrian President Bashar Assad, and Israel fears that as the fighting nears an end, Iran and tens of thousands of Shiite militiamen will turn their focus to Israel.

Lt. Col. Jonathan Conricus, a military spokesman, said Israel was not looking to escalate the situation. But he said troops will continue to be on "very high alert."

"Should there be another Iranian attack, we will be prepared for it," he said.

Iran's ability to hit back could be limited. Its resources in Syria pale in comparison to the high-tech Israeli military. Iran also could be wary of military entanglement at a time when it is trying to salvage the international nuclear deal.

Earlier Thursday, Israel said Iran's Al Quds force fired 20 rockets at Israeli front-line military positions in the Golan Heights. Conricus said four of the rockets were intercepted, while the others fell short of their targets. The incoming attack set off air raid sirens in the Israeli-controlled Golan, which was captured from Syria in the 1967 Mideast war.

Syria's state media said Syrian air defenses intercepted "hostile Israeli missiles" early Thursday that were fired over southwestern Damascus. Hours later, state-run Al-Ikhbariya TV broadcast a live feed of Syrian air defenses firing into the sky above the capital, and loud explosions and air defense firing were heard through the night.

Syrian activists reported Israeli airstrikes hitting targets near Damascus. One video posted online showed a large explosion and shrapnel flying in the air. Residents reported loud sounds that rocked their buildings. It was not immediately clear what was hit.

Al-Ikhbariya TV said Israel also targeted military posts in southern Suweida province, including an air base, and struck near Homs in central Syria. The state TV station said the attacks were foiled.

Iranian officials offered no immediate comment on Israel's claim about the missile fire. Iranian state media reported on the attack and the subsequent Israeli strikes in Syria, relying on foreign news reports.

Syrian media earlier said the hostilities began with Israeli fire at Syrian positions in southern Syria from across the border. Pro-Syrian media said Syrian missiles then fired at Israeli forces. One TV station, Beirut-based Al-Mayadeen, said at least 50 missiles were fired from Syria at Israeli forces in the Golan Heights. Al-Ikhbariya TV said missiles targeted 10 Israeli positions.

Syrian media said it was the first time in years that Syrians had fired at Israeli forces in the Golan Heights.

Late Tuesday, Syrian state media said Israel struck a military outpost near the capital of Damascus. The Britain-based Syrian Observatory for Human Rights said the missiles targeted depots and rocket launchers that likely belonged to Iran's elite Revolutionary Guard, killing at least 15 people, eight of them Iranians.

Last month, an attack on Syria's T4 air base in Homs province killed seven Iranian military personnel. On April 30, Israel was said to have struck government outposts in northern Syria, killing more than a dozen pro-government fighters, many of them Iranians.

Israel considers Iran to be its most bitter enemy, citing Iran's hostile rhetoric, support for anti-Israel militant groups and development of long-range missiles. President Donald Trump's withdrawal from the international nuclear agreement with Iran, with strong support from Israel, has further raised tensions.

Israel and Iran have appeared to be on a collision course for months.

In February, Israel shot down what it said was an armed Iranian drone that entered Israeli airspace. Israel responded by attacking anti-aircraft positions in Syria, but an Israeli warplane was shot down during the battle.

Israeli Prime Minister Benjamin Netanyahu traveled to Moscow on Wednesday to meet with President Vladimir Putin and discuss military coordination in Syria.

Russia has also sent forces to Syria to back Assad. But Israel and Russia have maintained close communications to prevent their air forces from coming into conflict.

Together with Putin, Netanyahu toured a parade celebrating the anniversary of the World War II victory over the Nazis and then met the Russian president at the Kremlin for consultations.

After 10 hours together, Netanyahu said he conveyed Israel's obligation to defend itself against Iranian aggression.

"I think that matters were presented in a direct and forthright manner, and this is important. These matters are very important to Israel's security at all times and especially at this time," he said.

Israel's military went on high alert Tuesday and bomb shelters were ordered open in the Israeli-controlled Golan Heights following reports of "irregular activity of Iranian forces in Syria." After an uneventful night, the military on Wednesday called on residents to return to "full civilian routine," meaning studies and excursions would continue as usual, although the shelters would remain open.

___

Associated Press writers Sarah El Deeb and Zeina Karam in Beirut contributed to this report.