Washington:  Trying to persuade a sceptical Congress to support sending more troops to Iraq, President George W. Bush warned that if the US fails, sectarian violence could spill over into an 'epic battle' between Sunnis and Shias in a wider regional conflict.

Bush has begun deploying the first of 21,500 more troops to Iraq as part of his revised strategy announced two weeks ago, but the Democratic-controlled Congress and some members of Bush's Republican Party steadfastly oppose the plan.

"If American forces step back before Baghdad is secure, the Iraqi government would be overrun by extremists on all sides," Bush warned.

"We could expect an epic battle between Shia extremists backed by Iran, and Sunni extremists aided by Al Qaeda and supporters of the old regime," he said.

"A contagion of violence could spill out across the country  and in time the entire region could be drawn into the conflict," he added in the State of the Union address Tuesday.

 "For America, this is a nightmare scenario," he said.

Bush's speech before a joint session of Congress comes as he faces the lowest job approval ratings of his president, mainly because of the unpopular war in Iraq. Bush said there was still time to reverse the violent trend in Iraq and prevail, but noted it requires the perseverance of the American people.

"This is not the fight we entered in Iraq, but it is the fight we are in," Bush said.

"Every one of us wishes this war were over and won. Let us find our resolve, and turn events toward victory," he said.

Democrats, who won control of Congress in the Nov 7 elections by campaigning on changing course in Iraq, want Bush to instead begin withdrawals of US troops.

Confronting the sharp criticism his plan has faced, Bush said that after a review of his policy, the best solution was to send more troops into Iraq to improve security in Baghdad and go after Sunni insurgents and terrorists operating in al-Anbar province.

Bush urged Democrats and Republicans to work together and reminded members of both parties who are now critical of his policy in Iraq that some of them voted to authorise the use of force before the March 2003 invasion.

"We went into this largely united in our assumptions, and in our convictions," Bush said.

"And whatever you voted for, you did not vote for failure. Our country is pursuing a new strategy in Iraq - and I ask you to give it a chance to work," he said.

 
Bush announced his plan Jan 10. Touching on it again, he said US support for the Iraqi government was not open ended and urged the Iraqis to take more steps to reduce sectarian bloodshed.

Bush has also warned Iran for supporting Shia attacks against Sunnis and said that Shia extremists backed by Iran were on the rise as terrorist threats and were as equally determined as their Sunni counterparts to create a Middle East governed by repressive regimes.

"The Shia and Sunni extremists are different faces of the same totalitarian threat," Bush said.

"But whatever slogans they chant, when they slaughter the innocent, they have the same wicked purposes," he said.

During the war on terrorism, most of the focus has been on the Sunni oriented Al Qaeda network that carried out the 9/11 terror attacks. But Hezbollah's stronghold on Lebanon has prompted greater concerns about Shia terrorism.

Bush also blamed Iran for backing the Lebanon-based Hezbollah. He said Hezbollah was second only to Al Qaeda in the American lives it has taken.

Bush said the war on terrorism is a 'generational struggle'and in a sign of determination to work with the newly empowered Democrats in Congress, the president proposed establishing a bipartisan advisory council to help develop strategies for defeating terrorism.

"We will show our enemies abroad that we are united in the goal of victory," Bush said.

"The evil that inspired and rejoiced in 9/11 is still at work in the world," Bush said, referring to the Sep 11 attacks.

"And so long as that is the case, America is still a nation at war," he said.