At least eight Iraqi police were killed and more than 60 wounded when rebels attacked a police station south of Baghdad, hospital officials have said.
A car bomb went off in a busy square in central Baghdad
The gun battle near the town of Salman Pak, in an area known as Iraq's "triangle of death", continued for over two hours, according to police sources.
Three people also died in a car bomb in the capital, and the bodies of 20 truck drivers were found south of Baghdad.
It comes as a recount of votes cast in the country's historic election began.
The latest attacks - which also led to the death of an Iraqi in Baquba, north of Baghdad - follow a brief lull after the election at the end of last month.
Amid fears that such mounting violence will mar this month's Shia festival, the interim government has announced the borders will be sealed for five days.
Police said the attack in Salman Pak began when a car bomb exploded in the morning.
A police convoy, which went in search of the insurgents, was then attacked with mortars and rockets in a fierce gun battle.
Thursday's bomb blast in Baghdad happened in Tahrir Square, a busy district in the centre of the city, shortly after a US army convoy passed through the area.
US military officials said there were no US casualties but at least three Iraqis are thought to have been killed.
Iraqi police said they have also found the bodies of 20 truck drivers in their burnt out vehicles south of the capital.
It is thought their convoy, carrying sugar to food warehouses, was attacked at least two days ago.
At least nine Iraqis died on Wednesday, including a correspondent for a US-funded Arabic TV station.
The government announced the closure of Iraq's borders for five days, starting next week, to boost security ahead of a Shia religious festival, Ashura.
At least 170 people died in multiple suicide attacks during the festival last year in Baghdad and Karbala.
Meanwhile poll results had been due on Thursday, but a recount of 300 contentious ballot boxes means the provisional tally could still be days away.
Partial election results suggest the Shia United Iraqi Alliance list is in the lead, with a coalition of Kurdish parties in second place.
The Kurdish leader, Jalal Talabani, has told the BBC he expects a tough battle over the constitution that the new Iraqi parliament is to draw up.
Mr Talabani, who is widely thought to have a good chance of becoming Iraq's next president, said there were likely to be sharp differences over the relationship between religion and the state.
He said Kurds would reject the demand of some Shia Muslim groups for Islam to become the basis of Iraqi law.