Faris al-Azzawi, a spokesman for the provincial health department, told Agence France-Presse that at least 14 people were killed in the blast. A further 64 were wounded.
Two men are believed to have carried out the attack, reported the BBC. One insurgent jumped out of the ambulance as it approached the Facilities Protection Services building in the heart of the city and opened fire on the guards. (The FPS is responsible for protecting government institutions.) The second man drove "very fast" toward the compound's main entrance, a witness, Saad al-Qiasi, told The New York Times.
"We felt that life was over and it was Judgment Day," he said. "Everything collapsed."
The explosion also damaged nearby buildings, including a women and children's hospital, reported AFP. Three young children and their teacher were also wounded at a nursery school, a provincial official told the news agency.
Another suicide car attack in a nearby town today killed at least three people and injured 15 more, the Los Angeles Times reported. Among the wounded were Sadiq al-Hussaini, deputy governor of Diyala province, and three of his bodyguards. The official was visiting pilgrims trekking on foot from Baghdad to the holy city of Karbala for the Shiite religious observation of Arba'een.
CNN noted that Sunni insurgents may launch more attacks during the 40 days of Arba'een, in an attempt to further whip up sectarian tension in Iraq.
Today's blasts came just a day after a suicide bomber blew himself up during a police recruitment drive in Tikrit, Saddam Hussein's hometown, killing at least 65 people and injuring 150 more, according to The Associated Press. That was the country's deadliest attack since the Oct. 31 siege of a Christian church in Baghdad, which left 52 worshippers dead. It's also the bloodiest strike since Prime Minister Nouri al-Maliki's political faction secured enough seats to name a new cabinet on Dec. 21, ending nine months of stalemate.
No group has yet claimed responsibility for any of this week's attacks, but the Times noted that the tactics used at Tikrit echoed previous suicide bombings by the Islamic State of Iraq -- a group affiliated with al-Qaida in Iraq. Both Baquba and Tikrit are located inside an area known as the Sunni Triangle, a stronghold of Iraq's insurgency. The Associated Press speculated that al-Qaida-aligned Sunni groups might have launched the attacks in the two cities to discourage fellow Sunnis from cooperating with security forces.
Others suggest that attacks on government facilities help to undermine popular support for Maliki, whose strongman persona and promises to restore stability helped secure his re-election in March.
"High-profile security breaches ... serve to puncture this law-and-order image that Maliki and his new government are trying to promote," Sean Kane, Iraq program officer for the United States Institute of Peace and a U.N. official in Baghdad from 2006 to 2009, told Time magazine. "Insurgent groups are certainly aware of this, and while high-profile attacks are growing less frequent, they are at least in part intended to embarrass and discredit the new government."
"I'm asking the security forces, isn't it enough?" Mutashar al-Samaraie, a member of parliament, asked during a debate in the chamber on the Tikrit bombing, according to the Times. "Isn't it time to take into account the previous events and attacks that have killed thousands of Iraqis?"
Former Vice President Tariq al-Hashimi also called for a review of security policies. ''The army and police recruiting centers have become attractive targets that are easily reached,'' Hashimi said in a statement cited by the newspaper.