The air raids early Wednesday hit positions in a rural area northwest of the capital, said the Britain-based war monitoring group Syrian Observatory for Human Rights.

Syrian state news agency SANA, citing a military source, said one Syrian soldier was killed and three others wounded in an Israeli strike on a military position near the capital.

"Today at 01:30 (2230 GMT) the Israeli enemy carried out an air aggression with missile bursts from northern Galilee, targeting a unit of our air defence forces in the Nabi Habeel area," the military source said.

"Our air defence countered some of the missiles, which caused one martyr and wounded three soldiers."

The Observatory on Wednesday morning said the number of wounded had risen to five, two of them in grave condition.

The strikes targeted Hezbollah rocket and ammunition depots in a mountainous area near the town of Zabadani close to the Lebanese border, destroying them and causing casualties, it said, without providing a toll.

Observatory head Rami Abdel Rahman said pro-Iran groups use the heights around Zabadani to store weapons and ammunition.

"Hezbollah uses (the area) as a storage spot before transporting weapons and ammunition into Lebanon," he said.

Israel refused to confirm or deny the strike.

"We do not comment on foreign media reports," an army spokesperson told AFP.

Israel has launched hundreds of strikes in Syria since the start of the civil war in 2011.

It has targeted government troops, allied Iranian forces and Hezbollah fighters.

It rarely confirms details of its operations in Syria, but says Iran's presence in support of President Bashar al-Assad is a threat to which it will continue to respond.

In the night of Thursday to Friday last week, Israeli missile strikes on Syria killed at least six Iran-backed fighters in the Masyaf district of Hama province, the Observatory said.

One of the missiles, which were fired from Lebanese airspace, also targeted a government-run research centre where surface-to-surface missiles are developed and stored, the Britain-based watchdog said.

Repeated Israeli air strikes against positions of Hezbollah and other pro-Iran groups in Syria in November killed more than 50 Tehran-backed fighters, most of them non-Syrian.

Syria's war has killed more than 380,000 people and displaced millions since starting in 2011 with the brutal repression of anti-government protests.