Bombs caused most of the casualties - including homemade blasts in the former Taliban stronghold of Kandahar and a neighboring province that together killed 20 civilians.
A roadside bomb and gunfire attack in western Afghanistan killed three Americans, while another roadside bomb killed two Americans in the east, said Chief Petty Officer Brian Naranjo, a spokesman for the U.S. military command in Kabul. No other details were available.
Taliban militants also staged suicide attacks - and came under attack themselves.
Coalition and Afghan forces on Saturday killed 11 militants during an overnight raid in northern Kunduz province, said Abdul Razaq Yaqoubi, the provincial police chief.
The operation targeted Taliban fighters who helped foreign fighters and suicide bombers infiltrate the region, said Capt. Elizabeth Mathias, a U.S. military spokeswoman.
She said "a number" of militants were killed after the forces exchanged fire. Roadside bomb-making material, ammunition and rocket-propelled grenades were found at the compound, she said. The raid did not appear to be connected with the kidnapping of a New York Times reporter and his Afghan colleague in the province this month, officials said. British commandos freed the Western reporter last week but the Afghan and a commando died in the operation.
The abductions followed a NATO airstrike on two stolen fuel tankers that appeared to have killed some civilians, officials said. Officials estimated about 70 people died in the strike.
Civilian casualties have dogged the U.S. and NATO mission in Afghanistan since the 2001 invasion, and have been repeatedly criticized by the Afghan government.
In Kabul, the capital, an American service member and an Afghan police officer got into an argument because the American was drinking water in front of the Afghan police, who are not eating or drinking during the day because of the Muslim fasting month of Ramadan, said the district chief, Abdul Baqi Zemari.
The police officer shot the American and seriously wounded him, while other American troops responded and seriously wounded the police officer, Zemari said.
Lt. Robert Carr, a U.S. military spokesman, confirmed an incident between Afghan police officers and a U.S. police mentoring team. He could not provide information on the conditions of the two men.
Authorities reported a string of deadly militant attacks in the south and east.
In Kandahar, two suicide bombers on a motorbike tried to attack an office of the country's intelligence agency on Saturday. Officers and the bombers traded gunfire. One bomber blew himself up and killed an intelligence officer, while the other bomber's explosives went off but didn't kill anyone, said Kandahar deputy provincial police Chief Fazel Hamid Sherzad.
Also in Kandahar, six civilians were killed by a homemade bomb Friday in Maiwand district, said district police Chief Bashir Hamad.
In neighboring Uruzgan province, 14 civilians were killed Friday when their vehicle hit a roadside bomb in Churra district, the Interior Ministry said.
Roadside bombs planted by militants are usually aimed at NATO or Afghan troops, but hundreds of civilians have been killed by them.
A Taliban ambush, meanwhile, killed six private security guards working for a construction company in the eastern province of Kunar on Saturday, said Gen. Khalilullah Ziayi, the provincial police chief. Ten guards were wounded, he said.
Also in the east, a suspected militant rocket attack killed three civilians in Sabari district of Khost, said Wazir Pacha, spokesman for the provincial police chief.
Four police were killed in Nangarhar late Friday when militants attacked a border police checkpoint, said Ahmad Zia Abdulzai, spokesman for the governor.
In eastern Paktika province, a suicide bomber detonated his explosives in Bermel district. Only the bomber died, the Interior Ministry said.
Associated Press writer Noor Khan in Kandahar contributed to this report.