British Prime Minister David Cameron on Wednesday accused Hizbullah and its main regional ally Iran of supporting the Syrian regime's violent crackdown on the country's uprising.

Cameron told lawmakers in the House of Commons that both were offering backing to Syrian President Bashar Assad.

Hizbullah denied on Wednesday accusations that it had shelled the Syrian area of al-Zabadani with Katyusha rockets, deeming such claims as “silly and laughable.”

It said in a statement: “These accusations are part of a campaign to incite the public against the party.”

Syrian security forces on Wednesday killed thirteen people across the country, “including two army deserters, two women and a man who died under torture,” activists said.

Nine people were killed in the central opposition bastion Homs, two in the restive countryside around Damascus, one in the northwestern province of Idlib and another in the northern province of Aleppo, the Local Coordination Committees, the main activist group spurring protests on ground, said.

European Union foreign ministers are set to slap fresh sanctions on Syria next week, adding 22 individuals and eight companies to an existing blacklist, EU diplomats said Wednesday.

"As long as the repression continues we will step up our restrictive measures," said an EU diplomatic source speaking on condition of anonymity.

Syria's state-owned media on Wednesday accused Qatar of arming and financing opponents of President Bashar Assad's regime.

Qatar's call to send Arab troops to the country "falls within the framework of the negative role played by Qatar since the start of this crisis... through the financing of armed groups," the Tishrin newspaper charged.

Beijing on Wednesday defended the Arab League's widely criticized observer mission in Syria, as the U.N. Security Cocil struggled to agree on a resolution on Damascus' crackdown on dissent.

China, a permanent veto-wielding member of the Security Cocil, urged both sides to cooperate with the Arab League, saying the security situation in Syria had improved since it began its mission there.

The Muslim Brotherhood has rejected an Iranian proposal to play a leading role in Syria's government in exchange for President Bashar al-Assad staying in power, one of its leaders told Al-Hayat newspaper.

Iranian intermediaries proposed that the Brotherhood "lead a government (in Syria) on condition we give up our demand to replace Bashar al-Assad," the group's deputy secretary, Mohammed Farouq Tayfour, told the London-based daily.

Foreign Minister Sergei Lavrov on Wednesday defended Russia's trade with Syria amid growing controversy over a mysterious shipment that reportedly delivered a supply of arms to Damascus.

Lavrov was asked to address criticism from Washington's U.N. Ambassador Susan Rice that followed reports that the shipment brought munitions to President Bashar Assad's forces amid their crackdown on protesters.

Russia warned Wednesday that a military strike on Iran would be a "catastrophe" with the severest consequences which risked inflaming existing tensions between Sunni and Shiite Muslims.

"As for the chances of this catastrophe happening, you would have to ask those constantly mentioning it as an option that remains on the table," Foreign Minister Sergei Lavrov said when asked on the chances of military action.

U.S. President Barack Obama on Tuesday decried continued and "unacceptable" levels of violence in Syria and pledged to redouble international efforts to force President Bashar al-Assad to step down.

Obama also thanked King Abdullah II of Jordan in the Oval Office for being the first Arab leader to call for Assad to go, after talks that also focused on Jordanian efforts to revive Israeli-Palestinian peace talks.