European Union foreign ministers discussed Wednesday whether to lift an arms embargo on Syria, in order help the opposition and are expected to take a decision in mid-February.

Speaking at the close of talks between the ministers, EU foreign policy chief Catherine Ashton said the bloc would "examine the system we have in place" ahead of their next February 18 meeting "to understand what we can do and can't do."

U.S. Vice President Joe Biden will discuss the carnage in Syria in meetings on Saturday with Russian Foreign Minister Sergei Lavrov and Syrian opposition chief Moaz al-Khatib, the White House said.

Biden will hold the meetings, and also see U.N.-Arab League envoy to Syria Lakhdar Brahimi at the Munich Security Conference on a trip that will also include talks with leaders of Germany, France and Britain.

The White House on Thursday warned Syria not to transfer weapons to Hizbullah, as tensions mounted following reported Israeli raids on a military research center and a Lebanon-bound weapons convoy.

"Syria should not further destabilize the region by transferring weaponry to Hizbullah," said Ben Rhodes, a U.S. deputy national security adviser.

Syria threatened Thursday to retaliate over what it says was an Israeli air raid, as Damascus allies rushed to denounce the strike which threatened to take the conflict beyond Syria's borders.

Israel maintained a stony silence over Syria's claims, as well as over separate reports that its jets had hit a weapons convoy near the Lebanon border.

Arab League chief Nabil al-Arabi on Thursday condemned a suspected Israeli air strike inside Syria a day earlier, saying in a statement that it violated the territory of a sovereign Arab state.

"This Israeli aggression... is a clear violation of the territory of an Arab state and of its sovereignty, going against the U.N. charter and the rules of international law," Arabi said.

Syria's main opposition chief on Thursday condemned President Bashar Assad's regime for its failure to take action against an Israeli air strike a day earlier.

"Shame on you, O regime of Bashar Assad, that the Israeli warplanes have come and your jets are only focused on destroying mosques and universities, and to kill civilians," Syrian National Coalition chief Moaz al-Khatib said.

Fierce clashes raged on Thursday between soldiers and rebel fighters on the southern outskirts of the Syrian capital as army tanks pounded the area, a monitoring group said.

"Fierce battles pitted troops against rebels on the road linking Damascus to Daraa, in the Qadam district and in Daraya," said the Syrian Observatory for Human Rights, which relies on a network of activists, doctors and lawyers.

Iran's foreign minister on Thursday condemned what he called Israel's "brutal aggression" against Syria, following claims by Damascus that the Jewish state's air force had hit a military research center.

"There is no doubt that this aggression is part of a Western and Zionist strategy to push aside the success of the Syrian people and government to return to stability and security," Ali Akbar Salehi said in a statement.

U.S. Ambassador Maura Connelly visited on Thursday the UNHCR registration center in Beirut during which she underscored President Barack Obama’s recent announcement of nearly $29 million in humanitarian assistance for Lebanon to support the refugees.

During her visit, Connelly “met with UNHCR Country Representative Ninette Kelley and with Syrian families who have sought protection in Lebanon from the continuing violence in Syria,” said a U.S. embassy statement.

Syria's main opposition group was to met Thursday in Cairo, a day after a surprise statement from its chief that he was willing to hold talks with regime officials, a Syrian National Coalition member said.

"This meeting was organized well before the Syrian National Coalition leader, Moaz al-Khatib, made his statement," SNC member Samir Nashar told Agence France Presse.