A suicide bomber rammed an ambulance packed with explosives into a security headquarters on Wednesday, killing 14 people in the second major attack against Iraqi forces in as many days.

Another suicide attack in a nearby town killed two others and wounded a top provincial official, shattering a relative calm in Iraq since the formation of a new government by Prime Minister Nuri al-Maliki last month.

"I was on my way to the market close to the building when I saw the ambulance arrive at the entrance," 53-year-old Sumaya Sabr, who suffered wounds to her head in the first blast, said from her hospital bed in Baquba, capital of Diyala province and site of the first attack.

"The guards tried to speak to the driver, and when they got close to the ambulance, it blew up. I can't remember anything else -- I woke up in the hospital."

The blast killed 14 people and wounded 120 others, according to Faris al-Azzawi, a spokesman for the provincial health department.

The morning bombing in central Baquba, a restive and ethnically mixed city north of Baghdad, targeted an office of the Force Protection Service (FPS), the agency responsible for securing government buildings.

The explosion also damaged nearby buildings, including Al-Batool women and children's hospital, an AFP journalist said.

Three young children and their teacher were also wounded at a nursery school, an official at Diyala Operations Command said.

Local officials imposed a vehicle curfew on Baquba, not allowing any cars in or out, and security forces cordoned off the scene of the blast.

The operations command official, speaking on condition of anonymity, said the FPS office had received a call from an individual purporting to work for the provincial health department, notifying them that an ambulance would be arriving, helping the attacker approach his target.

About 90 minutes later in the nearby town of Ghalbiyah, a suicide bomber blew up his explosives-filled car in the midst of a crowd of Shiite pilgrims, killing two people and wounding 15 others, Azzawi said.

An official in the provincial security command confirmed the death toll but said 16 people were wounded.

Among the wounded were Diyala deputy governor Sadiq al-Husseini and three of his bodyguards, and two media employees of a local satellite channel, Diyala TV.

Husseini was visiting with worshippers as they gathered ahead of commemorations for Arbaeen, which marks 40 days since the anniversary of the death of the revered 7th century Shiite Imam Hussein.

"I was in the procession tent when a VIP arrived with several cars and guards around him," said Zaid Essam, one of the wounded pilgrims, speaking from Baquba hospital.

"When he came close to the tent, an unmarked car suddenly came from the opposite side, trying to enter the tent to target him. But, because there were several obstacles protecting the tent, the car exploded outside and everything was thrown into the air."

Diyala was an Al-Qaeda stronghold as recently as 2008. While violence has dropped off dramatically both in Diyala and nationwide since then, the province remains one of Iraq's least secure.

The attacks came a day after a suicide bomber detonated an explosives-packed vest in the midst of a crowd of police recruits in Tikrit, also north of Baghdad, killing 50 people and wounding up to 150.

It was the deadliest attack to hit Iraq in more than two months, and the first major strike since Maliki named a new cabinet on December 21, ending nine months of stalemate after March elections.

Despite forming a government a month ago, Maliki has yet to name an interior, defence or national security minister, leaving him temporarily in charge of Iraq's entire security apparatus.

Tikrit's police chief Colonel Ibrahim al-Juburi and the head of the city's emergency response squad, Brigadier General Mohammed Majeed, were fired in the aftermath of the blast.

Maliki condemned the Tikrit attack, saying "terrorists" had once again targeted the innocent.

"Once again the terrorists returned to their usual tactics of killing the innocent and targeting the brave young people who wanted to serve their country and defend it," he said.