Insurgents attacked Afghan and international forces Friday with rocket-propelled grenades and guns, NATO forces said in a statement. The troops called in air support, forcing the militants to withdraw. They are being pursued, the statement said.
Col. Greg Julian, a spokesman for U.S. Forces in Afghanistan, confirmed that three of the dead service members were Americans. The nationalities of the other two were not immediately known because NATO typically waits for countries to release such information.
The Taliban have vowed to increase ambushes and other attacks as an additional 21,000 U.S. troops flood into Afghanistan this summer in an attempt to stem the group's resurgence and bolster security for August presidential elections.
In a sign that electioneering itself is likely to be chaotic, Afghanistan's top vice president broke away from the president to join a competing ticket, a spokesman for the ticket said Friday.
Former warlord Gul Agha Sherzai has snagged First Vice President Ahmad Zia Masood as his top deputy in his run against President Hamid Karzai, said Gul Khalid Pushtoon, a lawmaker serving as spokesman for Sherzai.
Sherzai, now governor of eastern Nangarhar province, plans to file official papers today, Pushtoon said.
Sherzai, who met with President Obama when he visited Afghanistan in July, has a mixed reputation. He helped the U.S. oust the Taliban from southern Kandahar province in the first push against the militants, but he has also been accused of heavy-handed rule and corruption in the aftermath.
A government spokesman, Waheed Omar, said he had not yet been informed of Masood's decision but that the government would not stand in his way.
"Masood is still the vice president of Afghanistan, but if he has decided that joining a different team will help, I don't think the president will have a problem because that is his constitutional right."
Spokesmen for Masood could not immediately be reached for comment.
Sherzai had in the past been a strong supporter of Karzai but Pushtoon said they are running against the president because they don't believe he's popular enough with the citizenry to hold onto the job.
A spike in violence and the accompanying civilian death toll has greatly eroded Karzai's popularity over the past year, along with conservatives arguing that he is puppet of Western powers.
"We think that President Karzai will not win the election, so therefore we want to keep the leadership in the region as well as improve the economy of the country," Pushtoon said.
Three Afghan army soldiers and 15 militants also died in clashes in the south and east Friday, U.S. military and Afghan officials said. No international casualties were reported in those incidents.