An attack by Israeli jets on military facilities in Syria has killed two Hezbollah fighters.
At least two members of the Shiite militant group, including a senior military figure were killed in Israeli air strikes in Syria over the weekend, sources told Al Arabiya News Channel.
Arabic media reports said that eight Israeli fighter jets were involved in the attacks.
Sunday's raid near the capital of Damascus hit nine targets, most belonging to Hezbollah, including a missile depot, said Rami Abdurrahman, head of the Syrian Observatory for Human Rights. He added that other members of Hezbollah may also have been killed.
Israel has launched attacks on Hezbollah positions in Syria and on the Lebanese border, including a strike in February that killed at least four militants. Hezbollah did not retaliate on that occasion, but has previously threatened to do.
Yuval Steinitz, Minister of Intelligence and Strategic Affairs, told Israel Radio: "We don't confirm, we don't deny," adding that his country's policy is to prevent "advanced weaponry getting to terrorist groups."
Syria has condemned the Israeli air force for striking in its territory at least six times over the past two years.
In Sunday's skirmishes, Israeli planes also flew over Lebanon several times, with Syria firing two surface-to-air missiles in retaliation, according to Lebanese al-Mayadeen TV.
The Syrian government wrote to the United Nations secretary-general and Security Council accusing Israel of "extending help and support to the armed terrorist groups in Syria," according to Sana.
They are demanding that the Security Council "severely condemn the Israeli attack and impose punitive sanctions on Israel due to its support of Syrian terrorist organizations."
Russia has also demanded an explanation from Israel about air strikes in Syria on Sunday.
"Moscow is deeply worried by this dangerous development, the circumstances of which demand an explanation," Russian foreign ministry spokesman Alexander Lukashevich said.
In a letter to the United Nations, Russia complained about Israel's "aggressive action" and demanded that such attacks should not happen again.