BAGHDAD, Iraq - A suicide bomber killed 30 Iraqis at an army recruiting center today in the northwest as Sunni-led insurgent groups continued their deadly campaign to intimidate voters before a weekend referendum on the country's draft constitution.

A special session of parliament was called for later this evening to vote on a last-minute breakthrough on the constitution reached by Shiite, Sunni Arab and Kurdish powerbrokers, reviving hopes of winning Sunni support for the charter at the polls.

The suicide attacker set off explosives hidden beneath his clothing at the first of two checkpoints outside the recruiting center in Tal Afar, where men were gathering to apply for jobs, said army Capt. Raad Ahmed and town police chief Brig. Najim Abdullah. They said at least 30 people were killed and 35 wounded.

The small town was struck Tuesday by another suicide bomber who killed 30 civilians and wounded 45 when he plowed his explosives-packed vehicle into a crowded outdoor market.

In August, U.S. and Iraqi forces conducted a major offensive in Tal Afar, 93 miles east of the Syrian border, claiming to have killed 200 insurgents and driven many others out.

In other violence today, three suicide car bombs and two roadside blasts killed one Iraqi and wounded 28 in Baghdad and the northwestern city of Baqouba.

An explosion set by insurgents also shut down an oil pipeline from the northern city of Kirkuk to refineries in Beiji, where it moves via the country's export pipeline to the Turkish port of Ceyhan, an official said.

The Kirkuk-Beiji pipeline is critical to Iraq's oil export operations, but that line is only open intermittently because of incessant sabotage.

In Baghdad, a government minister escaped an apparent assassination attempt when a convoy of cars preparing to pick him up at his office was hit by a suicide car bomb that wounded five bodyguards and five bystanders, police said.

Those and other attacks raised the death toll in the last 17 days to 425 in the militants' campaign to thwart Saturday's constitutional referendum, even as political leaders reached a compromise aimed at winning Sunni Arab support for the document.