Gunmen ambushed a bus carrying unarmed Iraqis to work at a U.S. ammo dump near Tikrit (search) on Sunday, killing 17 and raising the toll from three days of intensified and bloody insurgent attacks to at least 70 Iraqi dead and dozens wounded.

The attacks, focused in Baghdad (search) and several cities to the north, appeared to be aimed at scaring off those who cooperate with the American military — whether police, national guardsmen, Kurdish militias, or ordinary people just looking for a paycheck.

The violence came just weeks after the United States launched major offensives aimed at suppressing guerrillas ahead of crucial elections set for Jan. 30. Later Sunday, several small Sunni Muslim groups joined more influential Sunni clerics in demanding that the vote be postponed by six months.

Sunday's bloodshed began when gunmen opened fire at the bus as it dropped off Iraqis employed by coalition forces at a weapons dump in Tikrit, 80 miles north of Baghdad, said Capt. Bill Coppernoll, spokesman for the Tikrit-based U.S. 1st Infantry Division (search). Coppernoll said 17 people died and 13 wounded in the attack.

Survivors said about seven guerrillas were involved, emptying their clips into the bus before fleeing. The bodies of the victims were brought to a morgue too small to hold them all; some were left in the street.

About an hour later, a car bomber drove into an Iraqi National Guard checkpoint in Beiji, about 75 miles to the north, detonating his explosives-packed vehicle, Coppernoll said. Gunmen then opened fire on the position. Three guardsmen, including a company commander, were killed and 18 wounded, Coppernoll said.

Also Sunday, guerrillas ambushed a joint Iraqi-coalition patrol in Latifiyah, south of Baghdad, and attacked Iraqi National Guardsmen patrolling near Samarra, north of Baghdad. Two Iraqis were killed and 10 wounded.

The attacks seem to be an orchestrated campaign by Iraq's Sunni-led insurgency to strike any Iraqis who cooperate with the Americans. On Friday, a police station was hit and 16 men were killed. On Saturday, car bombs hit another police station, killing six, and a bus carrying Kurdish militiamen, killing seven.

The raids also appear designed to resupply the insurgents' arsenal. Rebels behind Friday's attack looted the police armory, and on Sunday, police said armed men stormed a station about 30 miles south of Fallujah and stole two police cars and a large cache of weapons.

That has not stopped the coalition from arming Iraqi forces. On Sunday, the U.S.-led Multinational Security Transition Command announced Iraqi security forces had received deliveries in November of 5,400 AK-47s, almost 2,000 9mm Glock pistols, 78 rocket-propelled grenade launchers and millions of rounds of ammunition — as well as body armor, night vision goggles, armored personnel carriers and four Russian-designed battle tanks.

Six U.S. soldiers have been killed since Friday as well. That number includes two soldiers slain Saturday during a patrol in Mosul's Palestine neighborhood, when they came under fire from insurgents shooting from two mosques and other buildings in the area, according to spokeswoman Capt. Angela Bowman. The U.S. military and Iraqi forces later raided a mosque and detained three suspects.

The raid drew several masked men onto the street in protest.

"I swear by God, I swear By God, I swear by God, our retaliation will be severe, God witness what I say!" a masked man shouted before speeding away in a car.

Jordanian terrorist Abu Musab al-Zarqawi's group, Al Qaeda in Iraq, claimed responsibility for several attacks Friday and Saturday. On Sunday, another militant group, Jaish Mohammed — Arabic for the Mohammed Army — issued a statement saying its fighters were lying low for "a few days" but planned more attacks against U.S. forces.

The group's statement, which could not be immediately verified, also warned Iraqis against aiding coalition forces and said they would be attacked with similar fury as that directed against the U.S. military.

The latest attacks on Iraqis cooperating with the interim government have been particularly brutal in their scale and have taken on a new urgency in light of the approaching vote.

The U.S.-led coalition had hoped its invasion of the insurgent hotbed of Fallujah last month would cripple the insurgency. Instead, the rebels appear to have scattered, and, after a brief lull, resumed their campaign.

The Iraqi Red Crescent Society withdrew from Fallujah on Sunday amid concerns over continuing insecurity, the organization's chief said. The Red Crescent, sister organization to the international Red Cross, set up operations there two weeks ago to assist Iraqi civilians who stayed behind during the fighting.

The Americans had also wanted Iraq's army and police force to play a larger role in calming the country before the elections. Instead, the homegrown troops have only shown how vulnerable they are to devastating and extremely demoralizing attacks.

Acknowledging that problem, the Pentagon decided Wednesday to raise troop levels from 138,000 to 150,000, more than were initially deployed for the war to oust Saddam Hussein last year, to help bring security for the vote.

While Iraq's majority Shiites are eagerly awaiting the election, the Sunnis oppose it, partly because the violence has been heavy in their areas west and north of Baghdad and voter registration there has not begun. About 40 small, mostly Sunni political parties met Sunday to demand the elections be postponed by six months, but stopped short of calling for a boycott.

President Bush, Iraqi Prime Minister Ayad Allawi and Iraq's Sunni president, Ghazi al-Yawer, have insisted the vote will be held as scheduled.