Maj. Gen. Aviv Kochavi, head of Israel's Military Intelligence, claimed Wednesday Tehran's main Arab proxy, Hezbollah in Lebanon, is also "providing Assad with intelligence, weapons and other means, recently with active involvement."
On Tuesday, Turkish customs officials, acting on a tipoff, intercepted four trucks allegedly carrying "military equipment" from Iran to Syria on the Iranian border.
Turkey, one of Assad's most prominent and vociferous critics, imposed economic sanctions on the Syrian regime in November, following the European Union and the 22-member Arab League.
Earlier Sunni-dominated Turkey imposed an arms embargo on Syria to protest the slaughter of anti-regime protesters across the country by Assad's powerful security services and military forces.
By U.N. count, more than 5,000 people have been killed since the insurrection broke out March 15, 2011.
On Wednesday, a ship believed to be carrying tons of weapons to Syria was intercepted when it made an unscheduled stop at Limassol on the southern coast of Cyprus, 70 miles west of Syria, a day earlier.
Cyprus state radio reported the freighter, the Russian-owned St. Vincent-flagged Chariot, was seized by customs authorities after they found "tens of tons of munitions" aboard.
The ship was released after the Russian owners promised it would not go to Syria.
The Cypriots did not say where the Chariot was headed when it left Limassol Wednesday.
But security sources said it could well make a dash for the Syrian port of Tartus, where the Russian navy has a base, or nearby Latakia.
Russia is Syria's main arms supplier and has stood behind its former Cold War ally in the current crisis. A Russian navy flotilla led by Moscow's only aircraft carrier recently visited Tartus in a show of solidarity with Assad.
Kochavi said Tehran and Hezbollah are determined to ensure the survival of Assad's regime that's dominated by minority Alawite Muslims.
Syria is Tehran's gateway to the Levant, where it can directly confront Israel from Lebanon through Hezbollah.
The loss of Syria would be a major strategic setback for Tehran's expansionist plans across the Arab world, which is dominated by the mainstream Sunni sect, and dramatically change the Middle East's geopolitical landscape.
If Assad is overthrown, Syria's Sunni majority, led by the radical Muslim Brotherhood, would likely take over.
"The radical axis is trying to retain its power and as time passes, Iran and Hezbollah increase their efforts to help the Assad regime survive," Kochavi said.
Assad, who succeeded his late strongman father, Hafez al-Assad, in June 2000, vowed Sunday he will never step down and insisted, despite the carnage, he had the support of Syria's people.
"We will declare victory very soon," he declared in a rambling speech at Damascus University that frequently verged on the delusional as the uprising becomes increasingly violent with army defectors turning their weapons on the regime.
Assad's speech, and his refusal to acknowledge the scale of the swelling opposition, domestic and international, to his regime after nearly a year of bloodshed reinforced observers' suspicions he may not actually be in charge any longer.
He has displayed this apparent denial of the harsh realities surrounding his position in the three other public appearances he has made since the uprising began.
Assad, a self-effacing former eye doctor in London whose iron-fisted father chose him to take over after his eldest son and heir apparent, Bassil, was killed in a 1994 car crash, has appeared uncomfortable as president of one of the Arab world's harshest dictatorships.
"Assad … never really wanted the presidency and has proved himself spectacularly ill-suited to it," observed international affairs analyst Simon Tisdall in The Guardian daily of London.
"The Syrian leader's state of mind is increasingly relevant as the … crisis deepens, with no sign yet of how or when it may be resolved.
"Critics say the president is isolated and out of touch with reality; others that he's a pawn, or even a hostage, in the hands of more powerful relatives and military figures," Tisdall observed.
"He certainly does not give the impression of being happy in his work."