At least 10 people have been killed in a series of roadside bombings in Iraq.
The Green Zone is heavily guarded by US and Iraqi forces
In one attack, at least five civilians died and more than 20 were injured when a bomb detonated near two buses in the western town of Ramadi.
A bomb also went off near the gates of the high-security Green Zone in Baghdad, where the Iraqi government and US military have their headquarters.
Two South African private security contractors died in the blast, US embassy officials said.
Three people in the same car, an American, an Iraqi, and another South African, were wounded in the attack.
The blast was followed by small-arms fire, and a plume of thick black smoke rose into the sky and US Apache helicopters circled overhead.
In Ramadi, suspected insurgents detonated a bomb near a US convoy, although only civilians - including a woman and a child - were killed, hospital officials said.
The US vehicles were not damaged.
Three people were killed in a separate bombing in eastern Baghdad, police said.
Meanwhile, the US military said it had killed about 37 insurgents in the latest phase of an operation near the Syrian border.
Operation Steel Curtain has entered a new phase, the military said, with troops battling insurgents in the town of Ubaydi on the Euphrates river.
"Five targets were struck by coalition air strikes resulting in an estimated 37 insurgents killed," a statement said.
"The insurgents were engaging coalition forces with small arms fire at the time of the strikes."
About 2,500 US and Iraqi soldiers have already staged raids in the towns of Husayba and Karabila.
Sunni Arab politicians say US-led military operations meant to uproot insurgents often cause heavy civilian casualties as well.