US Vice President Joe Biden celebrated the Fourth of July with his son and other American troops in Iraq on Saturday, a day after warning Iraqi leaders that US assistance will be jeopardized if the country reverts to ethnic and sectarian violence. After greeting over 200 US soldiers at a naturalization ceremony at one of Saddam Hussein's palaces at Camp Victory in Baghdad, Biden had lunch with the the 261st Theater Tactical Signal Brigade from Delaware, to which his son, Beau, belongs. "We did it in Saddam's palace," he said. "That SOB. is rolling over in his grave right now." Biden was wrapping up an unusually long three-day trip to Baghdad aimed at fostering political reconciliation, just days after US combat troops withdrew from Iraqi cities as part of a security pact that calls for a full withdrawal by the end of 2011. It was Biden's first visit as vice president and as Obama's new unofficial point man on Iraq, although he has been to the country several times as a senator. Biden planned to fly to the semiautonomous Kurdish region in northern Iraq later Saturday, but the trip was canceled due to heavy sandstorms. Meanwhile, on Friday, the vice president urged Iraqi Prime Minister Nouri al-Maliki to unite divided factions within Iraq, as concerns grow that a lack of political progress is fueling violence in Iraq. During a press conference with Maliki, Biden said, "Iraq has traveled a great distance over the past year, but there is a hard road ahead if Iraq is going to find lasting peace and stability. It's not over yetâ€¦There are still political steps that must be taken and Iraqis must use the political process to resolve their remaining differences and advance their national interest." "We stand ready, if asked and if helpful, to help in that process," he added. "I have seen very clearly the keen determination from the vice president and his administration to support Iraq ... and a great readiness to give us a lending hand and support anywhere we ask," he said.