By Tom Perry and Laila Bassam
BEIRUT (Reuters) - Supporters of Lebanon's Iran-allied Shi'ite group Hezbollah chanted "Death to the Saud family" as their leader railed against Sunni-led Saudi Arabia on Saturday in a sign of deepening hostility towards the U.S.-allied kingdom.
Speaking on Ashura, the day on which Shi'ites commemorate the death of Prophet Mohammad's grandson, Hezbollah leader Sayyed Hassan Nasrallah listed the Saudi leadership alongside traditional enemies Israel and the United States.
His armed group is an important player in the struggle playing out across the Middle East between the conservative Sunni Muslim-led government of Saudi Arabia and the Shi'ite Islamist government of Iran.
Thousands of its fighters are in Syria to support President Bashar al-Assad, taking part in a new ground offensive also backed by Iranian forces and Russian air strikes against insurgents who have received Gulf Arab backing.
The Saudi-Iranian rivalry is also playing out in Yemen, where Riyadh is leading a military intervention to try to restore President Abd-Rabbu Mansour Hadi's government and fend off what it sees as creeping Iranian influence.
Nasrallah condemned what he called the "U.S.-Saudi aggression" against Yemen. Thousands of black-clad supporters responded "Death to the Saud family! Death to the Saud family!". The chant is mostly reserved for Israel and America.
On the war in Syria, Nasrallah forecast victory for Assad and his allies. "Syria will not fall," he said.
Tens of thousands of Hezbollah supporters marched through the Shi'ite southern suburbs of Beirut. Some beat their chests in a show of self-punishment over the failure of Muslims to help in Hussein in battle against the Islamic ruler at the time, Yazid.
Nasrallah, who for security reasons typically speaks via video link, delivered the speech in person, the second day in a row he has appeared to address supporters. Security was tight in the area. Roads were closed to traffic.
Lebanon has also been an arena for Saudi-Iranian rivalry between Hezbollah and its Christian and Shi'ite allies on the one hand, and a rival alliance led by Sunni politician Saad al-Hariri, who is backed by Riyadh, on the other.
Nasrallah warned rival Lebanese politicians against waiting for Saudi Arabia and Iran to broker an end to a standoff that has paralyzed government and prevented the election of a new president.
"Don't wait for Iranian-Saudi dialogue. Matters in the region are getting more complicated," he said. "Don't await an American or Western initiative. Lebanon is beyond the concerns of foreign states. Lebanon is today left to its leaders."
(Writing by Tom Perry; Editing by Raissa Kasolowsky)