(Reuters) - Israel said it would not allow advanced weapons to fall into the hands of Hezbollah, after a raid on Syria that opposition sources said had hit an air force garrison believed to be holding Russian-made missiles destined for the militant group.

Israel has a clear policy on Syria and will continue to enforce it, officials said on Friday, after U.S. and European sources said Israel had launched a new attack on its warring neighbor.

Israel declined to comment on leaks to U.S. media that its planes had hit a Syrian base near the port of Latakia, targeting missiles that it thought were destined for its Lebanese enemy, Hezbollah.

"We have said many times that we will not allow the transfer of advanced weapons to Hezbollah," said Home Front Defense Minister Gilad Erdan, a member of the inner security cabinet which met hours before the alleged Israeli attack.

"We are sticking to this policy and I say so without denying or confirming this report," he told Israel Radio.

Israel is believed to have attacked targets in Syria on at least four occasions this year, the last time in July, with Prime Minister Benjamin Netanyahu saying he would not let sophisticated anti-aircraft, anti-ship and long-range missiles move from the hands of Syria to its Hezbollah ally.

One U.S. official and two European officials, speaking on condition of anonymity, said Israel was understood to have carried out the latest air strike on Wednesday.

The officials did not identify the target in Syria, but the U.S. official and one of the European officials noted that in the past such Israeli operations have destroyed missiles to prevent their transfer to Hezbollah.

A Latakia activist told Reuters that an explosion had rocked a garrison area that houses an air force brigade loyal to Syrian President Bashar al-Assad near Snobar Jableh village mid-afternoon on October 30.

Ambulance sirens were heard rushing to the scene, however, the activist, who calls himself Khaled, said there was a "total media blackout" about the incident.

The Britain-based Syrian Observatory for Human Rights quoted sources as saying there were four or five explosions at the base, but only limited damage reported. Al-Arabiya news network said SAM 8 anti-aircraft missiles were destroyed.

Former Syrian intelligence agent Afaq Ahmad, a defector now in exile in France, told Reuters on Thursday that contacts of his inside Syria, including in Latakia province, told him Russian-made ballistic missiles had been kept at the site that was attacked.

Assad's forces, backed by Hezbollah and Iran, are battling rebels in a civil war that has killed well over 100,000.

Khaled said Assad loyalists were frustrated about Israel's apparent impunity, recalling that the Syrian president had previously indicated Syria would respond to further attacks.

"Yet Israel keeps hitting us and there's no retaliation. So even the staunchest loyalists are getting very upset," he said.

IRRITATION BETWEEN ALLIES

Israel deliberately remains silent over its actions in Syria to keep a lid on tensions and try to avoid pushing Assad into a corner where he would feel compelled to respond.

Locals said they did not hear warplanes at the time of the blasts and there was initial confusion about who was behind the attack. One source, who declined to be named, said the limited damage on the ground suggested pinpoint missile strikes.

A foreign diplomat said that in the past the Israelis had succeeded in creating such confusion by using stand-off ordnance - missiles or gliding bombs that can be released many miles (kilometers) from the target.

There was clear irritation in Israel about the U.S. leaks, which analysts said might signal irritation in Washington over Israeli action at a time when Syria had bowed to international pressure and was dismantling its large chemical weapons arsenal.

"Washington is selling our secrets on the cheap," said top-selling Israeli daily Yedioth Ahronoth.

Still, the White House and Pentagon declined to comment on reports of the strike.

Israel has grown increasingly frustrated by U.S. policy in the Middle East, worried that President Barack Obama had been too soft on Assad and anxious over his rapprochement with Iran.

Uzi Rabi, director of the Moshe Dayan Center for Middle Eastern Studies at Tel Aviv University, said Israel had to make many calculations before approving attacks on Syria.

"Israel is sending a message to Assad, saying 'don't play games with us'. But Israel must also realize that the situation is becoming much more delicate than ever before because this is going against the U.S. diplomatic agenda," he said.

Rabi said the "working assumption" in Israel was that Assad was so focused on battling rebels that he could not afford to retaliate. However, he expected that Syria would seek international support to prevent Israeli air strikes.

A senior Israeli official, while declining to confirm any Israeli attack, did not expect Syria to respond.

"Assad is disarming (his chemical weapons) out of his own interests. He knows how to make the necessary distinctions," said the official, who declined to be named.

Technically at war with Syria, Israel spent decades in a stable standoff with Damascus while the Assad family ruled unchallenged. It has been reluctant to intervene openly in the 33-month Islamist-dominated insurgency rocking Syria, however is determined not to see Hezbollah profit from the unrest.

Hezbollah fought Israel to a standstill in a 34-day war six years ago. Israel has warned that any future conflict will be much more brutal.

(Additional reporting by Maayan Lubell and Dan Williams in Jerusalem, Erika Solomon in Beirut, Khaled Oweis in Amman, and Phil Stewart and Mark Hosenball in Washington; Editing by Giles Elgood and Vicki Allen)