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JERUSALEM — Israel's 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.

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 and that none of its warplanes was hit.

The IDF has struck dozens of Iranian military targets in Syria in response to the Iranian rocket attack against Israel. Quds force is behind attack and has played the initial price. IDF remains ready for various scenarios but does not seek to escalate the situation. pic.twitter.com/4rC8gHK2LG — Jonathan Conricus (@LTCJonathan) May 10, 2018

The blistering Israeli assault was by far the country's most intensive action in Syria since the civil war broke out there in 2011. Israel 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.

But with the civil war appearing to wind down, and Iranian forces looking to establish a foothold on Israel's doorstep, Israel has stepped up its response.

The Syrian Army Command said Israel's attack killed three people and injured two others. But the Syrian Observatory for Human Rights, a London-based war monitoring group, said the strikes killed at least 23 military personnel, including some non-Syrians.

Defense Minister Avigdor Lieberman said Israel would react fiercely to any further Iranian actions.

"We will not let Iran turn Syria into a forward base against Israel. This is the policy, a very, very clear policy, and we're acting according to this policy," he said. "If we get rain, they'll get a flood. I hope that we ended this chapter and that everyone understood."

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The IDF will not allow the Iranian threat to establish itself in Syria. The Syrian regime will be held accountable for everything happening in its territory — IDF (@IDFSpokesperson) May 10, 2018

Iranian state television broke its silence over the Israeli airstrikes late Thursday morning. The Israeli strikes were announced, with the information sourced to Syria's state-run SANA news agency. The broadcaster also described the Israeli attack as "unprecedented" since the 1967 Mideast war.

There was no immediate word on Iranian casualties.

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.

Syrian activists said the onslaught lasted more than five hours.

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 al-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 appears to be limited. Its resources in Syria pale in comparison to the high-tech Israeli military.

Earlier, 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.

However, Israeli schools opened as usual in the Golan Heights on Thursday morning.

Israel considers Iran to be its most bitter enemy, citing Tehran'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, and an Israeli warplane was shot down during the battle.

Thursday's conflagration came hours after Israeli Prime Minister Benjamin Netanyahu returned from a visit to Moscow, where he discussed concerns about Syria with Russian President Vladimir Putin.

The Israeli military said Russia had been forewarned of its strikes in Syria.

Russian Deputy Foreign Minister Mikhail Bogdanov later called the situation "very alarming," while French President Emmanuel Macron also appealed for calm.