US Secretary of State Condoleezza Rice in a surprise visit to Baghdad on Sunday said Iraqi leaders were more united than ever, as Shiite cleric Moqtada Al-Sadr has threatened an “open war” against the government. Rice also said that security in Iraq had improved but, during her stay in Baghdad's Green Zone, the heavily fortified area was rocked by an explosion which, according to a US official, could have been a rocket attack. More than 60 people, including 40 Shiite fighters, were reported killed since Saturday in clashes with security forces, Iraqi and US officials said. “I see a coalescing of a center in Iraqi politics in which the Sunnis, the Kurdish leadership and the elements of the Shiite leadership that are not associated with these ‘Special Groups' (alleged Iranian-backed Shiite groups) have been working better than at any time before,” she said. “It is indeed a moment of opportunity in Iraq thanks to the decision of the Iraqi prime minister and the unified Iraqi leadership.” But a top US general warned that the military would strike back. “I hope Moqtada Al-Sadr continues to depress violence and not encourage it,” said Major General Rick Lynch, commander of US forces in central Iraq. “I am giving my last warning and my word to the Iraqi government to take the path of peace and stop violence against its own people, otherwise it will be a government of destruction,” he said in a statement issued by his office in Najaf. “If it does not stop the militias that have infiltrated the government, then we will declare a war until liberation.” Soon after he made his statement, loudspeakers at mosques in Sadr's Baghdad bastion Sadr City blared out a call to arms and urged residents to “fight the occupiers.” Underscoring the threat of widening violence, the US military said it killed 40 militiamen in clashes in the cleric's Baghdad stronghold of Sadr City. A military spokesman called it the capital's “hottest night” in weeks. Meanwhile, nine university students and their driver were kidnapped Sunday near Baquba, north of Baghdad, when gunmen stopped their vehicle at a fake checkpoint. The gunmen also grabbed another man in a truck at the same checkpoint and took all of the hostages to an unknown location, police said. The students were returning to Diyala university after a weekend break. __