Russia cannot deliver advanced S-300 anti-aircraft missiles to the Syrian regime before 2014, Israel's defence minister asserted on Monday.
"We are following this matter with concern, but no deliveries have taken place. If they do take place, it will not be before next year," Moshe Yaalon told the parliamentary committee on foreign affairs and defence, in comments reported by army radio.
The minister did not elaborate on how he had arrived at his conclusions on this time frame.
On May 28, Yaalon warned that Israel would "know what do to" if Russia fulfilled the delivery of the S-300 system.
His words appeared to be a veiled allusion to military action along the lines of Israeli several strikes on Syrian soil earlier this year which targeted weapons from Iran destined for Hezbollah.
Addressing MPs at the committee, Yaalon reiterated that Israel was not interested in becoming embroiled in Syria's internal conflict, although he outlined four circumstances in which it would take action.
"We won't get involved in the civil war as long as they don't harm our interests, or if there is an attempt to transfer precise weaponry, especially to Hezbollah, an attempt to take over chemical weapons, or a heating-up of the border with continuing incidents of fire at our territory."
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Last month an Israeli army patrol in the occupied Golan Heights came under fire from Syrian regime forces over the armistice line. Israeli troops responded by blasting the Syrian army bunker from which the shooting came.
It was the latest of a number of incidents in the Golan in the past few months that have included apparently stray shells and small-arms fire from Syria.
On Friday, several Russian media outlets reported that Moscow had not yet delivered the S-300 surface-to-air missiles to Damascus and that the system could not be delivered this year.
The reports contradicted an interview Assad gave last week to Hezbollah's Al-Manar TV in which he implied that Moscow had already delivered some of the promised weaponry.
"All the agreements with Russia will be honoured and some already have been recently," he told the Lebanese station.
Deployment of the S-300 system would likely complicate any further Israeli airstrikes on Syria.
On the question of the state of the conflict in Syria, Yaalon said that regime forces now controlled no more than 40 percent of the country, and that rebels had seized "at least four neighbourhoods in Damascus."
He also confirmed Israel had opened a field hospital in the occupied Golan Heights to care for the wounded coming from Syria.
"It is a humanitarian gesture. But Israel does not intend to open a refugee camp" for civilians fleeing the fighting, he added.