Syria has summoned the head of a United Nations mission in the Golan Heights to protest against an Israeli air raid.
Damascus said the raid was a violation of a disengagement accord that followed the last major war between the two countries.
State media said Major General Iqbal Singha, head of the UNDOF peacekeeping force, was summoned to the Foreign Ministry where the protest was delivered.
UN Secretary-General Ban Ki-moon expressed "grave concern" over reports of the raid.
Earlier, Hezbollah condemned the attack, which it said targeted a Syrian research centre.
It said it was an attempt to thwart Arab military capabilities and pledged to stand by its ally President Bashar al-Assad.
"Hezbollah expresses its full solidarity with Syria's leadership, army and people," it said in a statement.
Sources said Israeli jets bombed a convoy near Syria's border with Lebanon, apparently targeting weapons destined for Hezbollah.
Syria denied the reports, saying the target had been a military research centre.
Hezbollah said the attack showed that the conflict in Syria, where Mr Assad is confronting an armed uprising, was part of a scheme "to destroy Syria and its army and foil its pivotal role in the resistance front [against Israel]".
The attack should make Mr Assad's opponents realise the danger of targeting Syria, Hezbollah said, and focus instead on "political dialogue as the sole basis to halt the bloodshed".
Ireland increases aid package to Syria
Meanwhile, the Minister of State at the Department of Foreign Affairs and Trade told the Dáil that Ireland has increased the value of its aid pledge to Syria by €4.7m, bringing the total contribution to €7.1m to date.
Joe Costello said the conflict in Syria was one of the most serious facing the entire world at the present time.
He said he had just returned to Ireland from a pledging conference on Syria in Kuwait.
He said Ireland would seek to promote a political settlement in Syria during the country's presidency of the EU and the dangers to the wider region were become more evident.