In a separate incident, in Nimroz province, a US marine was shot dead while on patrol, Elizabeth Mathias, a US military spokeswoman, said.
All the attacks took place on Thursday, the statement said.
The eight-year-old war in Afghanistan has been in its deadliest phase for foreign soldiers since July, when US and British forces launched their biggest offensives of the war.
There are now more than 100,000 Western soldiers in Afghanistan, about two-thirds of them American.
Stanley McChrystal, the most senior US army commander in Afghanistan, was expected to ask for thousands more troops in a request he will deliver to Washington this week.
He has said that without additional forces, his mission is likely to fail.
According to the independent icasualties website, which keeps a tally of military deaths in Afghanistan and Iraq, 371 foreign troops have died in Afghanistan so far this year, compared to 294 for all of 2008.