Iraq's landmark referendum has opened on time, but violence including a bombing at a Baghdad polling station has struck early in the voting day. 

Amid intense security, including a ban on all traffic on Saturday, voters dribbled into polling stations in Baghdad as they opened at 7am (0400 GMT).

Iraqi journalist Walid Khalid told Aljazeera from Baghdad that the voting process was going calmly though slowly.

He added, however, that turnout might pick up later as people sleep and wake up later during the fasting month of Ramadan.

Voter turnout was poor in tense areas such as Dura, al-Ghazaliya, al-Mansur and al-Amiriya, Khalid said.

Violence

The tight security was not enough to stop a roadside bomb from exploding near a polling station in western Baghdad on Saturday morning, wounding one police officer, police said.

The explosion occurred as the heavily guarded centre was opening at 7am, and no voters were there, said police Lieutenant Muhammad Kheyon.

The explosion on al-Madhif street in al-Amiriya area targeted an Iraqi police patrol stationed near a polling centre, injuring two officers seriously and damaging a police vehicle, Khalid told Aljazeera.

Police sources told Khalid that many explosive devices were planted along roads leading to polling centres in al-Amiriya and bomb experts had been called in.

Ramadi fighting

In Ramadi, fighting erupted at about 7am between a small group of fighters and US troops patrolling the mostly empty streets of the city, said police 1st Lieutenant Muhammad al-Ubaidi.

It was not immediately clear whether anyone was wounded.

South of Basra, three armed men attacked an empty polling station at 3am and were caught and arrested, said police Captain Mushtaq Kadhim.

On Friday night, four polling stations in southern Baghdad were fired upon, an Interior Ministry source said. No casualties were reported.

The attacks may cause delays that may push back the polling centres' scheduled closing time of 5pm. Up to 15 million Iraqis are set to accept or reject the new constitution.

Al-Qaida in Iraq has condemned the vote on the first post-Saddam Hussein charter. The group's leader, Abu Musab al-Zarqawi, has called on the minority Sunni Arabs to boycott.

Talabani appeal

In Baghdad's fortified Green Zone compound, where the Iraqi government headquarters is, President Jalal Talabani and Prime Minister Ibrahim al-Jaafari were two of the first to cast votes. 

"I voted 'yes' and I urge all Iraqis, no matter their different ethnicities and religions ... to vote 'yes' to the constitution," he said.

Talabani, a Kurd, said the choice was between political action and violence.

"The Sunni Arab brothers should understand that their aspirations will be achieved through political action, and not violence and terrorist acts," he said on Friday night on a television station popular with Sunnis.

Sunni Arabs, who dominated Iraq under Saddam, form the majority elements of the backbone of the uprising.

Their community largely opposes the constitution. 

Many of them fear that federalist provisions in the document will lead to the country splitting into three parts - with a Shia south and a Kurdish north holding the oil wealth and the Sunnis left empty-handed in the centre.

The Kurds overwhelmingly favour the document, as do the majority Shia.

The draft needs a simple majority of the 15.5 million registered voters for approval. But it can be blocked if two-thirds of voters in any three of the 18 provinces vote against it.

Sunni Arabs have a majority in al-Anbar, Salah al-Din, Nineveh and Diyala provinces.

Divided Sunnis

But the Sunnis are split, particularly since Shia and Kurdish legislators reached a deal with Sunni colleagues on Wednesday approving last-minute additions to the draft. 

These include the creation of a panel to consider amendments after general elections on 15 December.

Since then, six offices of the Islamic Party, which has come out in favour of the draft, have come under attack.

And a group with ties to al-Qaida issued a death threat via the internet against Islamic Party leaders.

The Association of Muslim Scholars, an influential Sunni group, has called on Iraqis to vote against the constitution.

If the constitution is approved, the December election will be held to form a new government.

In the event it is rejected, the government will be dissolved and elections held for a new parliament to write a new constitution.

Chief electoral officer Adil al-Lami has touted the referendum as "a major step towards a democratic Iraq".

"We saw last January when more than eight million people came out" to vote in general elections "that Iraqis are determined to have a voice in deciding the future of Iraq", he said.

More than 100,000 Iraqi police and soldiers will protect the more than 6000 polling stations over the day, with US and other foreign troops on standby.

PHOTO CAPTION

In this image released by the U.S. army, an Iraqi man is directed to a voting station by an Iraqi army soldier in Tal Afar, Iraq, Saturday, Oct. 15 2005. (AP)