A roadside bomb killed three US soldiers in the west of the country, and another killed two in the east, a Nato spokesman said.
Another roadside bomb in Kandahar province killed six civilians, the interior ministry and provincial governor said.
Two suicide bombers struck a detention centre for the National Directorate of Security in the provincial capital, killing a guard and child.
James Bays, Al Jazeera's correspondent, said the attack on the central Kandahar complex on Saturday appeared to be highly co-ordinated.
"A car drew up at the front of the offices, opening fire with guns and rocket-propelled grenades, clearing a path through the front gate to the intelligence department, killing a guard," he said.
A young girl living close by died of a heart attack at the start of the attack, he added.
Elsewhere, fighters killed four policemen in an attack on a patrol in Nangarhar province in the east of the country.
Six guards from a local security firm were killed when fighters attacked their office in nearby Kunar province.
In Farah province in the West, seven Afghan soldiers died in a lengthy gunbattle with Taliban fighters, and three civilians died when a rocket struck their home, provincial officials said.
The attacks came as Afghanistan is mired in a drawn-out dispute over election fraud that could test the patience of Barack Obama, the US president, and other Western leaders contemplating whether more troops are needed to defend its government.
Election authorities released new, near-complete preliminary results showing incumbent Hamid Karzai headed for a single round victory.
Our correspondent said: "Kabul is a city at the moment swirling with rumours.
"In terms of the results, we don't have a lot more information and I think that's causing some concern."
Preliminary results may be challenged by a UN-backed watchdog that says it has found proof of fraud and has begun voiding ballots from areas where Karzai won overwhelming support.
The latest results gave Karzai 54.3 per cent to 28.1 per cent for his main opponent, former foreign minister Abdullah Abdullah, with 92.8 per cent of polling stations tallied and another 2.15 per cent of them set aside due to suspected irregularities.
Our correspondent said the Independent Election Commission (IEC) and the separate Election Complaints Commission (ECC), have some disagreement.
"They will meet tomorrow to discuss how to carry out that recount, and it looks like its going to be a stormy meeting," he said.
If no one receives more than 50 per cent of the final count, the two candidates with the highest vote share will go into a run off poll.