BAGHDAD, Iraq - Six Iraqis and one U.S. Marine were killed today as insurgents clashed with U.S. troops and blew up a school slated to serve as a polling center, pre-election violence that followed the deadliest day for U.S. troops since the war's start. Another U.S. soldier died in an accident.

The Marine was killed and four others wounded when insurgents launched mortars at their base near Iskandariyah, about 30 miles south of Baghdad.

Australian officials announced that one of two car bombings on Baghdad's dangerous airport road Wednesday had injured eight Australian soldiers riding in a convoy escorting Australian government officials.

On Wednesday, 30 U.S. Marines and one Navy sailor died in a helicopter crash in bad weather in the western desert, and six U.S. troops were killed in insurgent ambushes. That made Wednesday the deadliest single day for Americans since the Iraq war began nearly two years ago.

Meanwhile, a Muslim youth group in Brazil issued an appeal for the kidnappers of a Brazilian hostage to release him. The appeal by the Alliance of Muslim Youth, broadcast on Al-Jazeera, noted that many Brazilians had opposed the Iraq war.

In a continuation of the pre-election violence plaguing the country, three Iraqis were killed and seven injured when a roadside bomb missed a U.S. convoy in Mahmoudiya area, 20 miles south of Baghdad this morning, according to the area's hospital director, Dawoud al-Taie.

Near Tikrit, a roadside bomb killed one Iraqi bystander and narrowly missed another passing U.S. military convoy, police said. The attack happened on a road near former dictator Saddam Hussein's hometown, about 80 miles north of Baghdad, said police Lt. Shalan Allawi.

In Samarra in the same region, armed men exploded a local school administration building this morning after first ordering the staff to leave, said police Lt. Qassim Mohammed. The destroyed building had been scheduled to be a voting center in Sunday's elections.

Sporadic clashes also erupted in Samarra today between U.S. troops and armed men, killing one Iraqi civilian and injuring another, Mohammed said.

U.S. forces also exchanged fire with insurgents in Ramadi, capital of the insurgent-plagued province of Anbar west of Baghdad.

In Baqouba, the body of a colonel in the former Iraqi intelligence during Saddam's era, Talib Minshid, was found in the city, according to a Baqouba hospital official, Mohammed Ali. Minshid had been abducted by armed men two days ago.

In the same town, one Iraqi police officer was killed and four others injured by a suicide car bomb today, according to Adel Mulan, the head of the Diyala provincial police force.

A U.S. soldier died from a gunshot wound early today on a base near Tikrit in what the American military command called an accident.

Another U.S. soldier was injured when his convoy was attacked early today near Kirkuk by small arms fire and a roadside bomb, said Master Sgt. Robert Powell.

And three Iraqis were wounded when a mortar shell landed on a house in the town of Khalis, 50 miles from Baghdad on Wednesday night, the hospital official said.

Just days before Sunday's crucial election, four Iraqi National Guard soldiers and one officer also were kidnapped Wednesday afternoon in Baghdadi, 90 miles west of Baghdad.

The kidnapping occurred after the Iraqi soldiers' car was stopped by insurgents at a checkpoint, according to witnesses at the scene who saw the incident.

On Wednesday, rebels launched a string of car bombs and attacks on polling centers across the country that killed at least 13 people.