BEIRUT -- Hezbollah's leader vowed Friday his militants would keep fighting in Syria "wherever needed" after the U.S. agreed to arm the rebels in the civil war, setting up a proxy fight between Iran and the West that threatens to engulf more of the Middle East.
U.S. President Barack Obama has deepened U.S. involvement in the conflict, authorizing lethal aid to the rebels for the first time after Washington said it had conclusive evidence the Syrian regime had used chemical weapons. Syria accused Obama of lying about the evidence, saying he was resorting to fabrications to justify his decision to arm the rebels.
The opposition forces, which have suffered key battlefield losses in recent weeks and were facing heavy fighting Friday in Syria's largest city of Aleppo, appealed for the weapons to be sent to them as soon as possible to swing the momentum to their side.
The two-year-old conflict, which the UN estimates has killed more than 90,000 people and displaced millions, is increasingly being fought along sectarian lines, pitting Sunni against Shiite Muslims, and is threatening the stability of Syria's neighbours.
Sheikh Hassan Nasrallah, chief of the Shiite Hezbollah group in Lebanon, appeared unwavering in his support for the regime of Syrian President Bashar Assad.
He signalled for the first time the Iranian-backed militant group will stay involved in the civil war after helping Assad's army recapture the key town of Qusair in central Homs province from rebels.
"We will be where we should be. We will continue to bear the responsibility we took upon ourselves," Nasrallah said in a speech via satellite to supporters in south Beirut. "There is no need to elaborate... We leave the details to the requirements of the battlefield."
Nasrallah appeared angry and defiant, saying the group has made a "calculated" decision to defend the Assad regime.
Hezbollah has come under harsh criticism at home and abroad for sending its fighters to Qusair, and Nasrallah's gamble in Syria primarily stems from his group's vested interest in the regime's survival. The Syrian government has been one of Hezbollah's strongest backers for decades, and the militant group fears if Assad's regime falls, it will be replaced by a U.S.-backed government hostile to Hezbollah.
Nasrallah said his group was the last to join the fray in Syria, after hundreds and perhaps thousands of Sunni fighters -- many of them from Lebanon -- headed to Syria in support of the rebels.
Assad's forces, aided by the Hezbollah fighters, captured Qusair on June 5, dealing a heavy blow to rebels who had been entrenched in the strategic town for more than a year. Since then, the regime has shifted its attention to recapture other areas in the central province of Homs and the city of Aleppo in the north.
Nasrallah did not say outright whether his group would go as far north as Aleppo, but he strongly suggested the group was prepared to fight until the end.
"After Qusair for us will be the same as before Qusair," he said.
The Britain-based Syrian Observatory for Human Rights said the fighting in Aleppo was concentrated in the city's eastern rebel-held neighbourhood of Sakhour, calling the fighting "the most violent in months." It said regime troops attacked the neighbourhood from two directions but failed to advance, suffering casualties.
The Obama administration is still grappling with what type and how much weaponry to send to the Syrian rebels, but the announcement buoyed the opposition forces, which are heavily outgunned and outmanned.
The commander of the main Western-backed rebel group said he hoped U.S. weapons will be in the hands of rebels in the near future.
"This will surely reflect positively on the rebels' morale, which is high despite attempts by the regime, Hezbollah and Iran to show that their morale after the fall of Qusair deteriorated," Gen. Salim Idris told Al-Arabiya TV.
U.S. officials said the administration could provide the rebels with small arms, ammunition, assault rifles and a variety of anti-tank weaponry such as shoulder-fired, rocket-propelled grenades and other missiles. The officials spoke on condition of anonymity in order to discuss internal administration issues with reporters.
-- The Associated Press