Voicing hope on Sunday that the document would be endorsed, US Assistant Secretary of State for Near Eastern Affairs David Welch told a Cairo news conference: "We see the political process in Iraq as providing an opportunity to the country to rebuild itself.
"We [the US government] don't see this as dividing Iraq, we favour a unified Iraq," Welch said.
He expressed hope that Iraqis would back the charter in Saturday's referendum.
"Each time they have faced a political choice, they have made it in a good way. They have had elections, they now will have a referendum on their new constitution and they will have a new election by the end of the year. I believe that is the path that Iraqis want to pursue."
Welch, who was speaking after talks with Egypt's President Hosni Mubarak, deemed that "Iraqis remain hopeful about their future" despite bloody anti-government attacks.
Sunni Arab groups urged voters on Saturday to reject the charter in the 15 October referendum because they fear the constitution could lead to the country's break-up.
Many Sunni Arabs, who make up about one-fifth of Iraq's population, oppose the draft because of federal provisions they fear will weaken the country and lead to an unfair distribution of oil wealth.
The document will have to be rewritten if more than two-thirds of voters in at least three of Iraq's 18 provinces vote "no", something Sunni Muslim Arabs might be able to achieve.
US and Iraqi officials believe that if more Sunni Muslims get involved in the political process, it will help isolate hardcore elements among groups opposed to the US presence in the country.
Welch, who arrived in Cairo late on Saturday night from Jedda in Saudi Arabia, will leave Cairo later on Sunday for talks in Israel, the Palestinian territories and Lebanon.
The US diplomat commended the work of former World Bank chief James Wolfensohn, also in Cairo for talks with Mubarak, to help iron out differences between Israel and the Palestinians after the Gaza pullout.
"I'm hopeful. The Gaza disengagement has proceeded well. There are some issues that remain to be worked out and Mr Jim Wolfensohn is very active in that respect," said Welch.
Wolfensohn (C) is charged with
developing the Gaza economy
Wolfensohn was appointed envoy for the Middle East Quartet [European Union, Russia, United States and United Nations] before Israel's evacuation of settlers and troops from Gaza, which was completed in September.
"I'm here through the day to meet with government officials," said Wolfensohn after talks with Mubarak during which he heard "his views on the current negotiations ... between the Israelis and the Palestinians which are so much supported by this country."
Open border demand
The Palestinians are pressing Israel to open up Gaza's borders into Israel and neighbouring Egypt, which took over security along its border with Gaza after the Israeli pullout.
But they refuse Israel's desire to retain control over what and who enters the Gaza Strip.
Wolfensohn later met with Egypt's Foreign Minister Ahmed Abu al-Gheit, Minister of Industry and Foreign Trade Mohammed Rashid and Army Chief of Staff Lieutenant-General Hamdi Wahiba.