BEIRUT – The leader of Lebanon's Hezbollah militant group said Tuesday that Syrian rebels will not be able to defeat President Bashar Assad's regime militarily, warning that Syria's "real friends," including his Iranian-backed militant group, were ready to intervene on the government's side.

In Damascus, a powerful bomb ripped through a bustling commercial district, killing at least 14 people and bringing Syria's civil war to the heart of the capital for the second consecutive day.

Hezbollah, a powerful Shiite Muslim group, is known to back Syrian regime fighters in Shiite villages near the Lebanon border against the mostly Sunni rebels fighting to topple Assad. The comments by Sheik Hassan Nasrallah were the strongest indication yet that his group was ready to get far more involved to rescue Assad's embattled regime.

"You will not be able to take Damascus by force and you will not be able to topple the regime militarily. This is a long battle," Nasrallah said, addressing the Syrian opposition.

"Syria has real friends in the region and in the world who will not allow Syria to fall into the hands of America or Israel."

Hezbollah and Iran are close allies of Assad. Rebels have accused them of sending fighters to assist Syrian troops trying to crush the 2-year-old anti-Assad uprising, which the U.N. says has killed more than 70,000 people.

Deeper and more overt Hezbollah involvement in the Syrian conflict is almost certain to threaten stability in Lebanon, which is sharply split along sectarian lines, and between supporters and opponents of Assad. It also risks drawing in Israel and Iran into a wider Middle East war.

Nasrallah said Tuesday there are no Iranian forces in Syria now, except for some experts who he said have been in Syria for decades. But he added: "What do you imagine would happen in the future if things deteriorate in a way that requires the intervention of the forces of resistance in this battle?"