Violence has been on the rise in both Afghanistan and Iraq
Eight soldiers have died on a bloody day for US forces in Iraq and Afghanistan.
Three died in a roadside bombing in northern Iraq - the US military's deadliest single incident in five months - and one died in Baghdad.
Four soldiers died in what was described as a "complex attack" in Kunar province, eastern Afghanistan.
Violence in Afghanistan is at a record high, while attacks have increased in Iraq since a US-led pull-back in July.
Exact locations of the attacks in Iraq were not given as next of kin had not yet been notified, but all four soldiers died in roadside bombings.
Earlier in the day, Iraqi police said a roadside bomb in the northern town of Amirli, south of Kirkuk, killed the local police chief and at least four of his colleagues.
A bomb attack targeting a senior Iraqi medical official in east Baghdad also left one ministry of health employee dead.
There were few details of the incident in which four soldiers were killed in eastern Afghanistan.
They were caught in a "complex attack", the Associated Press news agency quoted US army spokeswoman Capt Elizabeth Mathias as saying.
In Afghanistan, violence has surged to a record high eight years after the US-led invasion which toppled the Taliban.
Some 820 US soldiers are thought to have died in Afghanistan in those eight years.
In Iraq, violence has grown since the end of June when US-led forces withdrew from urban areas, leaving responsibility in the hands of the Iraqi police and army.
Casualty figures are still well below the worst levels of 2006 and 2007, when more than 2,000 Iraqi civilians were being killed in civil strife and by anti-US insurgents every month.
About 4,340 US troops have been killed in Iraq since the 2003 US-led invasion.