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US plans to arm Syrian rebels have raised fears in Israel that the weapons could fall into the wrong hands, but analysts played down the threat -- provided no big guns are involved.

Washington said last week that it would provide Syria's rebels with military support in the form of small arms after it determined that the Syrian regime had used chemical weapons.

US President Barack Obama on Wednesday declined to categorise the arms the US will send to the rebels.

"I cannot and will not comment on specifics on our programmes related to the Syrian opposition," Obama said, at a press conference in Berlin with German Chancellor Angela Merkel.

Two months ago, Israeli Prime Minister Benjamin Netanyahu urged caution over such plans saying it "presents the question of which rebels and which weapons?"

And Israel's former deputy foreign minister Danny Ayalon has repeatedly warned that such a move would be a "mistake."

Other Israeli officials have drawn parallels with Afghanistan in the 1980s, when US supplies to Mujahedeen fighting the Russians found their way years later to Al-Qaeda.

Analysts said the extent of the threat to Israel depended on what weaponry was involved and where it ended up.

"If it means the provision of small arms and ammunition, such as RPGs and mortars... I don't think that's going to mean anything for Israel, and am not even sure it will for the rebels," said Jonathan Spyer, senior researcher at the Global Research in International Affairs Centre in Herzliya, near Tel Aviv.

Even "if some of those weapons reach the hands of extreme jihadist elements, such as Al-Nusra Front (in the Golan Heights) ... it is not a major strategic threat, but rather an irritant," he said.

Dr Jacques Neriah, former adviser to late prime minister Yitzhak Rabin, agreed that it would depend on the type of weaponry the US intends to provide to the rebels.

"Anti-tank weaponry is problematic because in the past, weapons given by the US to allies farther east found themselves in Lebanon or in Gaza," he said, alluding to arms given to the Mujahedeen in Afghanistan, some of which Israel believes ended up in the hands of Lebanon's Shiite Hezbollah movement and Islamist groups in the Gaza Strip.

"There's a good chance these weapons might find their way to Gaza," he added.

Daniel Nisman, an intelligence specialist at Tel Aviv-based risk consulting firm Max Security Solutions, agreed.

"Advanced weapons like anti-tank capabilities... might increase the level of concern from Israel, maybe even objection," he said.

Neriah said Syria's rebels in any case did not need anti-tank weapons or small arms to gain the upper hand in the more than two-year conflict.

"They've plundered the depots of the Syrian army... and got their hands on weapons, tanks and armoured personnel carriers and so on."

More useful would be strategic advantages like electronic intelligence capabilities or a no-fly zone, Neriah said, but stressed the latter was unlikely to be implemented given Damascus ally Russia's opposition to such a move.

The provision of small arms, in the meantime, would have little effect, Neriah argued: "There's no logic in giving them these weapons."

Nisman disagreed.

"Any aid can help, even if it's light aid," he said.

"Take the example of Qusayr," which the Syrian regime recaptured with help from its ally Hezbollah earlier in June.

"The Assad regime and Hezbollah initially thought it would be a quick campaign, but it ended up taking longer and costing more casualties. This was because they encountered more resistance within an urban setting from rebels with small arms using ambushing tactics.

"That kind of limited military aid can help rebels bog down Hezbollah and the Assad regime in an urban setting like say in Aleppo," Nisman said.

Analysts said victory in Syria would boil down to who receives the most foreign military aid.

"Compared to the aid (the regime) is receiving from Russia and Hezbollah, (the proposed US provision) doesn't match," said Mike Herzog, former head of strategic planning in the Israeli army and a fellow at the Washington Institute for Near East Policy.

Victory is a "question of international aid, and who gets more. Right now, Assad's regime is getting more, whether from Hezbollah, Iran, or Russian drone support," Nisman said, referring to reports Moscow was giving Assad unmanned spy aircraft.

Recent rebel losses "have coincided with a drop (in aid)," he said.