Iraqis cast their ballots Saturday in the country's landmark referendum on a draft constitution amid tightened security.

Iraqi President Jalal Talabani Prime Minister Ibrahim al-Jaafari cast their votes early Saturday in the heavily fortified Green Zone in central Baghdad, which houses Iraqi government offices and the US Embassy.

A few people were seen heading in the early hours to Baghdad's voting stations as Iraqi security forces heavily guarded the streets.

Up to 15 million people are expected to participate in the vote. Advocates hope the constitution will unite the country, but Iraqis are divided on the draft document, which has seen repeated revisions.

Over 6,000 polling stations throughout Iraq opened to about 15.5 million eligible voters out of Iraq's population of 26 million. The poll is expected to end at 5:00 p.m. (1400 GMT).

According to the timetable of Iraq's political process, new elections will be held by the end of this year to form a new parliament if the charter is approved in the referendum.

However, if two thirds of voters in any three of the 18 provinces say no in the referendum, the charter will be vetoed and the parliament then dissolved.

Talabani, a Kurd, and al-Jaafari, a Shiite Muslim, made a television speech late Friday, calling for a "yes" vote in the referendum.

Talabani also called on the Sunni Arab insurgents to lay down their arms and join the political process.

Most of Iraq's Shiites, about 60 percent of an estimated 27 million population, were expected to approve the charter, especially after Shiite spiritual leader Grand Ayatollah Ali al-Sistani called on followers to do so.

At the same time, Iraqis in the Sunni-dominated Salahudin province will possibly say "No" in the referendum, some residents told Xinhua on Friday.

"We insist on participating in the referendum to veto the draft," said Umer Hammash, a resident in the provincial town of Dhuluiyah.

"We will be human shields for the voting centers tonight, and we will go there after sunset to stay and protect the centers from whoever want to prevent the Sunnis from defeating the draft," he said.

Salahudin is one of the three main Sunni Arab provinces which are expected to veto the constitution if most of the more than 500,000 constituents said "No" to the draft.

On the eve of the referendum, streets in the main cities of the province were blocked by barricades for Saturday's referendum.

"The security operation would be 100 percent Iraqi, and we had experience from the past elections this year," Brigadier Issa Abd Muhmoud, head of the US-Iraqi Joint Coordination Center in Tikrit, told Xinhua.

Deputy Governor of Salahudin Abdullah Hussein Jebara was keen to say "No."

"It is the beginning to divide Iraq and waste its wealth," he argued.

Jebara said some 249 voting centers across the province have received their ballot boxes. Moreover, there are mobile voting centers touring in remote areas in the province where it would be difficult for residents to vote.

Residents of the mainly Sunni province were furious on Friday after the Iraqi Islamic Party, a leading Sunni party, called on Sunni Arabs to vote "Yes."

"The leadership of the party behaved against the Iraqi interest which disappointed many of the party's members," said Abdullah Abdul Rahman, a member of the party.

Despite pressure from Sunni Iraqis who oppose the charter, Salahudin Governor Hamad Hemood al-Qaissi still showed optimism.

"The province is ready for the referendum and I call on our people to actively participate," Qaissi told Xinhua.

"I support every word of the draft constitution," Qaissi said.

Sunni Arabs account for 80 percent of the province's population, plus the Turkman minority whose political leader in Tuz Khurmato said his people would reject the draft.

On the night before the vote, most parts of the Baghdad region were shut down by insurgent saboteurs.

Mahmoud al-Saaedi, spokesman of the Iraqi electricity ministry,said the insurgents attacked powerlines from the capital to the northern towns of Kirkuk and Baiji.

The blackout set in shortly after dusk, leaving the city cloaked in darkness except for a few scattered glimmering dots of light. Several hours later, power supply began slowly returning to the city.

Also on Friday, the White House hailed the upcoming referendum, describing it as "a historic moment in the history of Iraq."

"It is a hopeful moment for the entire region," White House spokesman Scott McClellan told reporters.

(Xinhua News Agency October 15, 2005)