The Syrian Observatory for Human Rights said an ammunition depot and several positions linked to Iran's military presence in Syria were among the targets.

Government media in Syria confirmed four casualties in the strikes, on which Israel did not comment.

"The Israeli enemy carried out an air assault at dawn... targeting several positions around Damascus," a military source was quoted as saying by the state news agency SANA.

"The investigation indicated that four soldiers were killed, three others injured and material damage noted."

The latest strike follows another near Damascus on April 14, without casualties, according to SANA.

The UK-based Observatory, which relies on a vast network of sources across Syria, said eight people were also wounded in the strikes.

The other four killed were not members of the Syrian military but belonged to Iran-backed militia, Observatory chief Rami Abdel Rahman said, adding he could not verify their nationality.

He said at least five separate sites were targeted in the latest Israeli raid.

AFP correspondents in the Syrian capital said they heard loud explosions.

Since the war broke out in Syria in 2011, Israel has carried out hundreds of air strikes inside the country, targeting government positions as well as allied Iran-backed forces and Shiite militant group Hezbollah.

- 'Not frozen' -

In early March, two officers from Iran's Revolutionary Guards were killed in Israeli strikes on targets in Syria.

The Islamic Revolutionary Guards Corps is the ideological arm of the Iranian military and holds considerable political and economic sway over the country.

The elite Quds Force is the Guards' foreign operations arm and is listed as a terror group by the US.

While Israel rarely comments on individual strikes, it has acknowledged mounting hundreds since 2011.

The Israeli military has defended them as necessary to prevent its arch-foe Iran from gaining a foothold on its doorstep.

The conflict in Syria started with the brutal repression of peaceful protests and escalated to pull in foreign powers and global jihadists.

It has killed nearly 500,000 people and displaced half of the country's population.

In a briefing to the UN Security Council on Tuesday, the UN's special envoy to Syria Geir Pedersen warned the conflict in Ukraine should not distract from the dire situation in Syria.

"Syria is a hot conflict, not a frozen one," he said.

He listed incidents that occurred this month in Syria involving the armed forces of Israel, Turkey, Russia and the United States.

"I worry that any of these flashpoints could be further exacerbated by heightened geopolitical tensions outside of Syria," Pedersen said.

Washington has indicated it was prepared to give Ukraine the means to fight Russia's invasion, prompting warnings from Moscow that arms deliveries to Kyiv risked sparking World War III.

Russia's military intervention in the Syria conflict in 2015 is what turned the tide in favour of President Bashar al-Assad, whose forces once only controlled a fifth of the country.