A mortar attack in southern Baghdad has killed at least 15 people and left dozens of

Iraqi father carries his injured son to a hospital in Baqouba, Iraq, February 26, 2006

others wounded, while a roadside bomb killed two U.S. soldiers in another sector of the Iraqi capital. U.S. officials say efforts by Iraq's political and religious leaders to avert a possible civil war could help forge a sense of national unity.

The specter of all-out sectarian violence has hung over Iraq since last week's bombing of a Shi'ite shrine and a subsequent flurry of reprisal attacks.

But President Bush's National Security Advisor, Stephen Hadley, offered hope that Iraqis will unite to fight terrorism, and in so doing, lay a foundation for political progress that solidifies democratic rule.

"What is really interesting is the response of the various communities in Iraq. You have seen statements from all of them condemning the violence and indicating their resolve that there needs to be calm, no resort to violence, and movement forwards towards a unified government, which really is what Iraq needs," said Hadley, speaking on CBS's Face the Nation program.

The national security advisor's hopeful assessment of Iraqi prospects for political progress is not shared by Michigan Senator Carl Levin, the ranking Democrat on the Senate Armed Services Committee.

Speaking on ABC's This Week program, Levin argued the Bush administration's open-ended commitment to maintaining U.S. forces in Iraq has allowed the country's leaders to put off tough decisions, and that Iraq needs to be told that U.S. patience is not without limit.

"Here is what I would say [to Iraq]: 'If, in the next six to eight weeks, you do not create a government of national unity, if you continue to squabble, then we [the United States] are going to have to reassess," he said. "We are going to look at whether or not it makes sense for us to continue to stay there, when you are not solving your political problem.'"

But Republican Senator John McCain of Arizona, also speaking on ABC, says U.S. patience is still required in Iraq, and that even a discussion of a possible troop withdrawal from Iraq would be counter-productive.

"Everything in the country [Iraq] we have learned over the last few years is [that it takes] two steps forward, then one step back," said Senator McCain. "We have a long way to go, and any talk of troops withdrawals, in my opinion, would be foolish. We [the United States] have made serious mistakes in Iraq, which have caused us enormous problems, and we have paid consequences. But in the long term, we still have to prevail there."

A recent Pentagon assessment of Iraqi troop readiness concluded the country currently has no army battalions capable of standing up to insurgents and terrorists on their own, but a growing number that can take the lead in counter-insurgency operations with U.S. support.