In a televised speech the Iranian president told a crowd that "God's promises have come true" and the United States' plans to reshape the Middle East had been ruined.
Tehran and Damascus may be the biggest winners from the 34 days of fighting in Lebanon, buoyed by the ability of their protege, Hezbollah, to withstand Israel's punishing assaults - and the growing popularity of Hezbollah across the Middle East.
Hezbollah has been left hampered by the war's resolution: the Lebanese army and international troops are to deploy in southern Lebanon.
So the truce has undermined the guerrillas' domination of the territory and its ability to attack Israel.
But the Shi'ite Muslim movement appears to have been strengthened inside Lebanon.
Syria and Iran ridiculed US hopes for eliminating the guerrillas and belittled Israel's high-tech military as useless against Hezbollah.
"The Middle East they (the Americans) aspire to ... has become an illusion," Syria's Bashar Assad said in a speech in Damascus.
"We tell them (Israelis) that after tasting humiliation in the latest battles, your weapons are not going to protect you - not your planes, or missiles or even your nuclear bombs ... The future generations in the Arab world will find a way to defeat Israel," Mr Assad added.
US dismisses Assad "bluster"
US State Department spokesman Sean McCormack described president Assad's broadside as “bluster” and sour grapes after Syria was excluded from any role in implementing the UN resolution designed to halt the fighting between Israel and Hezbollah.
"This sort of bluster notwithstanding, I think the Syrian government finds itself much more isolated right now than either one month ago or three years ago," Mr McCormack said.
"The facts are that, once this resolution is implemented, it is a strategic setback for Hezbollah, its patrons in Tehran, and as well as in Damascus.
"(Assad) finds himself in Syria, out of Lebanon, a place which it had used to, basically, take the riches and the bounty of the Lebanese people over a period of 20 years, abuse the Lebanese people over 20 years.”
Ahmadinejad: "God’s promises"
A few hours after Mr Assad spoke, Iran's fiery leader, Mahmoud Ahmadinejad, saluted Hezbollah for hoisting what he said was "the banner of victory" over Israel.
"God's promises have come true," Mr Ahmadinejad told a huge crowd in Arbadil in northwestern Iran.
"On one side, its corrupt powers of the criminal US and Britain and the Zionists .... with modern bombs and planes. And on the other side is a group of pious youth relying on God."
He said Hezbollah's fight had foiled US-Israeli plans to dominate the region.
Peres: Hezbollah a "foreign legion"
Speaking after meeting in Washington with US Secretary of State Condoleezza Rice, Israel’s Deputy Prime Minister, Shimon Peres, described the Lebanon-based Hezbollah militia as "a foreign legion" trained and armed by Iran.
"This is in fact today an Iranian armed division -- by training, by weapons, by command, by finance," Mr Peres said.
He estimated that Iran had been spending more than US$100 million a year to arm and train the militia, which sparked the latest Middle East conflict by capturing two Israeli soldiers in a cross-border raid on July 12.
"They're a paid Iranian force, no matter what the name," he said, asserting that Iranian instructors were working with the militia in Lebanon and that some Hezbollah combatants had received training in Iran.
Israel, backed by the United States, says much of Hezbollah's weaponry has come from Iran via Syria.
US: "A sad situation"
The US dismissed the claims by Syria and Iran of a Hezbollah victory as shameful boasting.
"It is terrible that the president of Iran is trying to take advantage of this tragedy," David Welch, a senior US State Department official, said.
Both Iran and Syria are "trying to pile on popular emotion and anger at a time of tragedy for their own selfish advantage," the assistant secretary of state said at a news conference.
"I think it is a sad situation when leaders of other countries can stand on this rubble" that is the aftermath of the war in Lebanon and proclaim their vision, Mr Welch said.
Spy chiefs blacklisted
The US Treasury has blacklisted two senior Syrian intelligence officials, accusing them of sponsoring terrorism and destabilising Lebanon.
The Treasury named Major General Hisham Ikhtiyar, the former head of Syria's General Intelligence Directorate (GID), and Brigadier General Jama'a Jama'a, who used to command Syrian Military Intelligence (SMI) headquarters in Beirut.
"Until Syria takes concrete steps to become a responsible member of the international community, the United States will make known rogue actors supporting the country's destabilising agenda," said Pat O'Brien, the Treasury's assistant secretary for terrorist financing.