Hussam Ali, a police officer who witnessed the blast from a nearby guard post, said the attacker took advantage of the construction work to avoid the usually tight security and reach the main gate.
"The chances of success [in Iraq] are essentially zero because the Iraqi people have no voice"
Non Sequitur, Cadiz, Spain
Send us your views
"We were very cautious, but this time we were taken by surprise," he said. "The insurgents are inventing new methods to hurt us."
Elsewhere, another three people were killed and seven others wounded in a double mortar attack in the nearby Abu Chir district.
South of Baghdad, five people were killed and 30 others wounded in another truck bombing outside a small Shia religious site in the mixed sectarian town of al-Haswa, a police source said.
Also on Saturday, a suicide bomber blew himself up in a pastry shop in the northwestern Iraqi town of Tal Afar, killing eight people and wounding 10, the mayor of the town said.
Campaign against 'collaborators'
The blasts in Baghdad come a day after Salam al-Zubayi, one of Iraq's deputy prime ministers, was seriously wounded in a suicide bombing near his home, as armed groups appeared to be stepping up a campaign against those seen as collaborating with the US and the Iraqi government.
Al-Zubayi was in stable condition and was moved out of intensive care on Saturday morning, but remained under anesthesia at a US-run hospital in the Green Zone, Dhafer al-Ani, a Sunni legislator said.
Brigadier general Qassim al-Moussawi, a military spokesman, said he had visited al-Zubayi in the hospital and found him in good condition.
"The medical situation of Dr al-Zubayi is stable after he had a surgical operation to remove shrapnel from his lungs," al-Moussawi told state-run Iraqiya television in a telephone interview.
The Sunni Iraqi Accordance Front, the biggest Sunni parliamentary bloc to which al-Zubayi belonged, denounced the attempted assassination and said such attacks will not make Sunnis abandon the political process.
"Whether al-Qaeda or other organisations were behind such attacks, this will not force us to abandon our principles and firm stances in moving ahead with the political process," Amil al-Qadhi, a party official, said.
"Our decision was a strategic one and we do believe that our presence is very critical in this period and it is impossible to withdraw from the political process."
In other violence, the US military said three sectarian fighters were killed in an air strike in western Iraq and 12 suspects were captured in raids targeting the al-Qaeda in Iraq organisation.