TAL AFAR, Iraq — A U.S.-Iraqi force has punched deep into Tal Afar near the Syrian border, arresting 200 suspects in the sweep, including the most-wanted insurgent in the city.

Three-fourths of those arrested were foreign fighters, the Iraqi Army said yesterday.

Iraqi army Capt. Mohammed Ahmed said one of suspects was Amr Omayer, the commander of all insurgent operations launched from Tal Afar, where 70 percent is Sunni Muslim, the sect that dominates the Iraq insurgency.

Most of the estimated civilian population of 200,000 have fled this predominantly Turkmen city.

"We ordered the families to evacuate the Sunni neighborhood of Sarai, which is believed the main stronghold of the insurgents," Ahmed said, suggesting it soon would be targeted in a major push.

The U.S. military reported killing seven insurgents in the past two days.

The sweep in Tal Afar came as election officials tallied figures from three Sunni-dominated provinces, where the voter registration was extended a week in preparation for the Oct. 15 nationwide referendum on the new constitution.

"Turnout was unbelievable, and people were very enthusiastic, especially in Fallujah and Ramadi," said Farid Ayar, an electoral commission spokesman in Baghdad. Those cities are Sunni insurgent bastions in Anbar province, which stretches west from Baghdad to the Syrian, Jordanian and Saudi borders.

The large voter signup suggests minority Sunnis are mobilizing to defeat the draft charter, a marked tactical shift from January, when their boycott of the parliamentary election handed control of the 275-member National Assembly to Shiites and Kurds.

The new basic law was approved and sent to voters by a coalition of Shiites and Kurds, over the objections of Sunni representatives, who fear it would allow the country to split into sectarian and ethnic ministates. That could cut Sunnis out of Iraq's enormous oil wealth.

The very Sunni clerics who railed in January against an election "under foreign military occupation" are now urging their people to take part in both the referendum and the parliamentary balloting in December.

Rejection of the charter would mean elections in December for a new parliament under the rules of the interim constitution approved in March 2004. The new parliament would start the entire process of drafting a constitution from scratch.

Demographics are a big problem for the Sunni Arabs — an estimated 20 percent of Iraq's 27 million people.

Sunnis form the majority in four of the 18 provinces, but their numbers are overwhelming in only two, Anbar and Salahuddin. Under election rules, a no vote by a two-thirds majority in any three provinces would defeat the referendum.

In other developments:

• Police reported finding 17 bullet-ridden bodies near the capital. Fifteen were spotted close to Mahmoudiya, a heavily Sunni farming town 20 miles south of Baghdad. Two more bodies, blindfolded and handcuffed, were found on Baghdad's southern outskirts. The victims were not identified.

• The U.S. military announced the death Wednesday of a soldier assigned to the 2nd Force Service Support Group in an industrial accident at Camp Taqaddum near Fallujah, 40 miles west of Baghdad. At least 1,895 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

• In central Baghdad, a suicide car bomber yesterday targeted a passing convoy of private U.S. security agents, wounding three passers-by.