BAGHDAD, Iraq – Bombings struck four coalition and Iraqi military convoys and a provincial government office yesterday, killing at least eight people, including an American soldier and an Estonian trooper in the Baghdad area.

Coming a day after the bodies of nearly 50 Iraqi military recruits were found massacred, the bombings occurred as a U.N. agency confirmed that several hundred tons of explosives were missing from a former Iraqi military depot in an insurgent hotspot south of Baghdad.

The massacre of the unarmed Iraqi cadets headed home on leave suggests Iraqi insurgents have infiltrated Iraq’s security forces deeply enough to gain intelligence and make precision strikes of their own.

Although American officials say it’s too early to tell whether the cadets were set up, some American officers have long regarded Iraq’s security forces as susceptible to infiltration. Last week, defense officials in Washington described Iraq’s security forces as “heavily infiltrated” by insurgents.

“The police and military forces all have insurgents in them,” according to Lieutenant Colonel Jeffrey Sinclair of the 1st Infantry Division. “You don’t have a pure force.”

The massacre Saturday night near the Iranian border was the most dramatic of a growing number of precision attacks by rebels who appear to be operating with inside information on movements, identities, and future plans of Iraqi security forces.

Yesterday, a roadside bomb in western Baghdad killed one American soldier and wounded five, the American military said. An Estonian soldier died when a roadside bomb exploded at a market just outside Baghdad as his patrol went by, the Estonian military said. Five other Estonian soldiers were wounded.

A car bomb also targeted an Australian military convoy 350 yards from their country’s embassy in Baghdad, killing three Iraqi civilians and wounding nine people, including three Australian soldiers who suffered minor injuries, Iraqi and coalition officials said.

“This is the first time that…Australian vehicles have been attacked by direct enemy action,” an Australian Defense Force spokesman, Brigadier Mike Hannan, said in Australia’s capital, Canberra.

Jordanian terrorist Abu Musab al-Zarqawi’s group, renamed Al Qaeda in Iraq, claimed responsibility for the attack on the Australians in a statement posted on an Islamic Web site. It was impossible to verify the claim’s authenticity.

His group, formerly known as Tawhid and Jihad, has been blamed in numerous suicide car bombings and beheadings of foreign hostages, including deadly twin bombings inside Baghdad’s highly secured Green Zone, which houses the American and Iraqi leadership.

In near-simultaneous attacks yesterday in the northern city of Mosul, suicide car bombers struck provincial government offices and a military convoy, the American military said. Three government employees were killed and one injured at the offices and an Iraqi general was slightly injured in the attack on the convoy, a government spokesman said.