At least 13 people have died in an ambush on a minibus carrying workers to a US base in Baquba, Iraqi police say.
Baquba is a frequent target for insurgency violence
Gunmen in two cars targeted the bus as it travelled to al-Faris airbase, 60km north-east of Baghdad, officials said.
Ten people were killed by gunfire, and another three died when the bus careered into another car - possibly one of those used by the gunmen.
Iraq is still reeling from a blitz of bombings over the weekend in which scores of people lost their lives.
Iraqis working for coalition forces are frequent targets of anti-US insurgents in Iraq.
A report quoting the interior ministry says the minibus crashed into one of the attackers' cars, but the fate of the occupants is unclear.
There are also reports of a roadside bombing targeting a police patrol in Kirkuk, in Iraq's oil-rich north, that killed two people.
One of the dead was a policeman and the other a member of President Jalal Talabani's Patriotic Union of Kurdistan party.
BBC World affairs correspondent Nick Childs says the huge and mounting number of civilian casualties poses an enormous political challenge for the Iraqi authorities struggling to establish their credibility.
Interior ministers from Iraq and its neighbours are meeting in Turkey, where they are addressing concerns that violence and instability in Iraq could spread through the region.
At the start of the talks in Istanbul, Turkish Interior Minister Abdulkadir Aksu said there was an undeniable link between violence in Iraq and support from the outside.
He said the ministers would focus on how to improve Iraq's security internally and along its borders.
Iraqi Interior Minister Bayan Jabr is expected to demand that Iraq's neighbours take stronger action to stem the flow of money and recruits to insurgents. He has been especially critical of Syria, accusing it of playing host to militants.
Earlier, Prince Hassan of Jordan called for a broad-based Middle East conference on Iraq to be held, to prevent the fragmentation of the country. He told the BBC that Iraq was now in a state of civil war.