BEIRUT, Lebanon - Hezbollah leader Sayyed Hassan Nasrallah accused President Bush on Tuesday of creating chaos in Lebanon, rejecting his charge that the militant group and its allies were causing the violence.

Sectarian clashes in Beirut last week between pro- and anti-government supporters left seven people killed, bringing back memories of Lebanon's 1975-1990 civil war.

Addressing hundreds of thousands of Shi'ite Lebanese gathered in Beirut's southern suburb for the climax of the annual Ashura religious ceremony, Nasrallah challenged Bush's latest attack against the group and said the U.S. had ordered Israel to launch last year's war against Hezbollah guerillas.

On Monday, Bush accused Hezbollah and its allies Iran and Syria of stirring up the latest violence in Lebanon in a bid to topple its government and said "those responsible for creating chaos must be called to account."

"The one who fomented chaos in Lebanon, who destroyed Lebanon, who killed women and children, old and young in Lebanon, is George Bush and (Secretary of State) Condoleezza Rice who ordered the Zionists to launch the war on Lebanon," Nasrallah said in a fiery speech.

The July-August war killed nearly 1,200 people in Lebanon, mainly civilians, and 157 Israelis, mostly soldiers.

"The one who must be punished, who must be tried, is the one who ordered the launching of war on Lebanon. George Bush wants to punish you because you resisted, he wants to punish you because you won," Nasrallah said addressing a sea of black which converged on Beirut's southern suburb to commemorate the killing in battle of the Prophet Mohammad's grandson, Imam Hussein.

"George Bush knows ... and we reiterate to him -- and the whole world should hear --, that we are a nation that doesn't succumb and can't be humiliated."

'DEATH TO AMERICA'

Earlier, the crowd marched in Hezbollah's Beirut stronghold, rhythmically beating their chests in a sign of grief over Hussein's martyrdom and chanting "Death to America, death to Israel."

Some carried red, yellow and black flags with religious slogans. Others wore green headbands and chanted, "We will never be humiliated."

But this year the event takes place against a backdrop of heightened fears that a Lebanese political standoff could disintegrate into sectarian strife between Sunnis and Shi'ites, mirroring Iraq, which is on the verge of all-out civil war, and infighting between Palestinian factions.

In his third public appearance in as many days, Nasrallah warned "resistance groups" in the region against civil war.

"Today the biggest challenge facing all the resistance groups in Lebanon, Palestine and Iraq is to avoid slipping into civil wars and internal strife, as the nation's enemies want."

Ashura commemorates Hussein who was killed along with most of his family by Islamic ruler Yazid, whom Shi'ites remember as an oppressor and murderer. Hussein's death at Kerbala in AD 680 is a defining moment in the history of Shi'ite Islam.