Syrian President Bashar al-Assad has been quoted as saying Damascus has received the first shipment of an advanced Russian air-defense system whose delivery has riled Western governments.
Meanwhile, the main Western-backed opposition outside Syria has said it will not participate in peace talks while massacres in that country are continuing.
Hizballah-owned Lebanese television Al-Manar quoted Assad as saying in an interview due to be broadcast later on May 30 that the rest of the S-300 rockets shipment "will arrive soon."
Assad reportedly added that the army is holding "the balance of power" in the conflict after scoring "major victories" against rebels.
Russia has defended its decision to deliver S-300 antiaircraft missiles to the Syrian government, saying they would help deter any foreign military intervention.
The S-300 surface to air missile system is capable of hitting aircraft, cruise, and ballistic missiles. Each launcher vehicle carries four missile containers.
Experts have said the possible use of the S-300 missiles could be a "game-changer" in the conflict.
The delivery of such missiles raises fears of further tension with Israel, which last month launched air strikes inside Syria to destroy weapons believed to be destined for Hizballah.
Israeli Energy and Water Minister Silvan Shalom told public radio that there is "no need to provoke an escalation" but that Israel will not allow the transfer of strategic weapons to groups like Hizballah. "In that case," he said, "we would have to act."
Earlier on May 30, a Syrian rebel leader accused Hizballah of "invading" his country.
In a BBC interview, General Selim Idriss claimed that more than 7,000 fighters from the Lebanese Shi’ite militia allied to Assad were participating in attacks on the rebel-held town of Qusair.
In Istanbul, the opposition Syrian National Coalition announced it will not attend a proposed peace conference in Geneva next month while allies of Assad's regime are waging war alongside government forces.
The opposition acting chief, George Sabra, told reporters: "The National Coalition will not take part in any international conference or any such efforts so long as the militias of Iran and Hizballah continue their invasion of Syria."
Russian Foreign Minister Sergei Lavrov earlier accused the opposition group of seeking to thwart peace efforts.
"One gets the impression that the [opposition's Syrian] National Coalition and its regional sponsors are doing everything they can to prevent a political process from starting," Lavrov said, "and by any means including dishonest work over public opinion in the West, to achieve military intervention in Syria."
Interfax news agency quoted a Russian Foreign Ministry source as saying Russian, U.S., and UN officials will meet on June 5 to discuss ways of bringing the warring sides in Syria together for a peace conference.
With reporting by AFP, AP, Reuters, and Interfax