The Syrian Observatory for Human Rights said the missiles struck a military base in the province of Hama late Sunday, in an assault it said bore the hallmarks of an Israeli operation.

"At least 26 fighters were killed, including four Syrians," the monitor said, adding that the main target of the missile strike was the base of the regime's 47th Brigade.

"The others are foreign fighters, a vast majority of them Iranians," said Rami Abdel Rahman, the head of the Britain-based war monitor.

"Given the nature of the target, it is likely to have been an Israeli strike," he said, adding that strikes also hit an air base in nearby Aleppo province where surface-to-surface missiles were stored.

Syrian state media late Sunday had denounced a "fresh aggression" following reported raids by "enemy missiles".

Israeli Intelligence Minister Yisrael Katz told army radio on Monday morning that he was "not aware" of the latest strikes.

But, he said, "all the violence and instability in Syria is the result of Iran's attempts to establish a military presence there. Israel will not allow the opening of a northern front in Syria."

The latest strikes came amid heightened tensions in Syria after Damascus and its ally Iran accused Israel on April 9 of conducting deadly strikes against a military base in the centre of the country.

At least 14 soldiers, including seven Iranians, were killed in the strike on a military base in Homs province.

Days later, on April 14, the United States, France and Britain bombarded several Syrian regime military positions in response to a suspected chemical attack on the rebel stronghold of Douma which killed dozens, according to rescue services.

Syria remains technically at war with neighbouring Israel, which is concerned at the growing presence of Iranian forces and those of Tehran's Lebanese ally Hezbollah on Syrian territory.

Israeli Defence Minister Avigdor Lieberman vowed in an interview Thursday to strike at any attempt by Iran to establish a "military foothold" in Syria.

"If they attack Tel Aviv, we'll strike Tehran," he told the Arabic-language Elaph news website.

US Secretary of State Mike Pompeo, who met with Israeli Prime Minister Benjamin Netanyahu on Sunday in Tel Aviv, lashed out at Iran's "ambition to dominate the Middle East".