BAGHDAD, Iraq - Insurgents determined to wreck Iraq's constitutional referendum killed more than 40 people and wounded dozens in a series of attacks today, including a suicide car bomb that ripped apart a crowded market in a town near the Syrian border, police said.

U.S. and Iraqi officials have repeatedly warned that the insurgents would step up their attacks to undermine Saturday's referendum, a crucial step in Iraq's democratic transition.

In the deadliest attack in nearly two weeks, a suicide car bomb exploded at about 11 a.m. in a crowded open market in the northwestern town of Tal Afar, killing 30 Iraqis and wounding 45, said Brig. Najim Abdullah, Tal Afar's police chief. U.S and Iraqi forces routed insurgents in a major offensive there last month.

He said all the victims appeared to be civilians since no Iraqi or U.S. forces were in the center of Tal Afar, which is 260 miles northwest of Baghdad.

Insurgents also used two suicide car bombs, three roadside bombs and four drive-by shootings in the capital on Tuesday to kill a total of 14 Iraqis; 29 were wounded, police said.

The worst attack involved a suicide car bomb that exploded about noon at an Iraqi army checkpoint in a busy area of western Baghdad, killing eight Iraqi soldiers and one civilian and wounding 12 soldiers, said police Capt. Qassim Hussein.

The violence came four days ahead of Iraq's key vote on the draft constitution, which Kurds and the majority Shiites largely support and the Sunni Arab minority rejects. Sunnis are campaigning to defeat the charter at the polls, although officials from all sides have been trying up to the last minute to decide on changes to the constitution to swing Sunni support.

In another development, a top election official said today that Iraqi law will allow Saddam Hussein and thousands of other detainees who have not been brought to trial to vote in the referendum.

However, Abdul Hussein Hindawi, one of the eight highest-ranking officials on the Independent Electoral Commission in Iraq, also said the organization was still awaiting a full list from the Interior Ministry and the U.S.-led coalition of the detainees who should be allowed to receive copies of the draft constitution and to vote at Abu Ghraib prison and several other U.S. detention centers.

"All non-convicted detainees have the right to vote. That includes Saddam and other former government officials. They will vote," said Abdul Hussein Hindawi, one of the eight highest-ranking officials on the Independent Electoral Commission in Iraq, in a telephone interview.