BAGHDAD (AP) - Vice President Joe Biden spent the Fourth of July with his son and other American troops in Iraq on Saturday, while the Iraqi government spokesman publicly rejected the American's offer to help with national reconciliation, saying it's an internal affair.

Biden took a break from politics and presided over a naturalization ceremony for 237 U.S. troops from 59 countries in a marble rotunda at one of Saddam Hussein's former palaces at what is now Camp Victory, the U.S. military headquarters on the western outskirts of Baghdad.

He then had lunch with the 261st Theater Tactical Signal Brigade from Delaware, to which his son, Beau, belongs. Beau Biden stood in the back as his father greeted the troops. In telling the brigade about the naturalization ceremony, the vice president used some of his characteristic colorful language.

"We did it in Saddam's palace, and I can think of nothing better," he said. "That S.O.B. is rolling over in his grave right now."

Biden's unusually long three-day trip to Baghdad, which began late Thursday, was aimed at fostering political reconciliation after U.S. combat troops withdrew from Iraqi cities as part of a security pact that calls for a full withdrawal by the end of 2011.

Government's spokesman Ali al-Dabbagh's comments were in response to an appeal Biden made a day earlier for Iraqis to do more to bring the country's deeply divided factions together and his offer of U.S. help. Biden also warned Friday that U.S. assistance may not be forthcoming if the country reverts to ethnic and sectarian violence.

"The political situation won't accept that the United States intervenes in an internal issue, whether that issue is reconciliation, relations between various Iraqi groups or between the (self-ruled Kurdish) region and Baghdad," al-Dabbagh said on Iraqi state TV.

"The U.S. administration is concerned about the absence of progress on some political issues in Iraq and this is clear," he added. "But the prime minister said that these are internal issues and it is the Iraqis who will handle the matter and the interference of non-Iraqis in these issues will create unnecessary complications and problems."

Al-Maliki is trying to use the U.S. withdrawal to build support before Jan. 30 general elections and his spokesman's remarks were likely aimed at an Iraqi public impatient with the American presence. But they also signaled a growing assertiveness by Iraqis as the U.S. dominance in the country wanes with its pullback of troops.

Al-Maliki's office also said the Iraqi government is committed to the national reconciliation process but excluded Saddam's ousted Baath Party, saying "it is responsible for the destruction inflicted on Iraq."

It was Biden's first visit to Iraq 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.

In closed-door meetings Friday, the vice president pressed al-Maliki and other political leaders to do more to bring Iraq's divided factions together, as concerns grow that a lack of political progress is fueling violence in Iraq.

While Biden stressed America's commitment to Iraq's progress in his public remarks, a senior U.S. official said the vice president warned the Iraqis that America won't be able to stay involved if Iraq falls back into the cycle of sectarian violence that pushed the country to the brink of civil war in 2006 and 2007.

Al-Maliki has been criticized for failing to take advantage of security gains to make progress in overcoming disputes between Shiites, Sunnis, Kurds and other groups, leaving a stalemate that has threatened to erupt into violence and stalled a key oil bill and other legislation.

Biden's visit and his new position overseeing the U.S. administration's Iraq policy reflect growing concern about a recent rise in violence after a series of bombings that killed scores of people.

A roadside bomb exploded in Youssifiyah, south of Baghdad, on Saturday, killing one civilian and wounding five others, police said.

Violence remains at low levels in Iraq compared with previous years, but a series of bombings that killed scores of people raised concerns about the run-up to the parliamentary elections.

At least 447 Iraqi civilians were killed in June, double the toll from the previous month, according to an Associated Press tally.

Sunni lawmaker Hashim Yahya called on Biden to pressure neighboring countries to stop interfering in Iraqi affairs, a reference to mainly Shiite Iran, which the U.S. military also alleges is supporting violence in Iraq.

But, he said, Biden could not force Iraqi factions to resolve their differences.

"Biden can do nothing to impose concessions or national reconciliation on the Iraqis unless the politicians decide to put an end to their disputes," he said. "But we welcome any efforts by Biden to help Iraqi politicians resolve their differences for the sake of Iraq."

Associated Press Writer Sameer N. Yacoub contributed to this report.