Separately, three police and four tribal elders were killed in a roadside bombing, police said.
The first helicopter crash, during a routine operation, did not result in any fatalities, said ISAF spokesman Capt. Justin Brockhoff. Two died in the second crash, ISAF said.
Taliban spokesman Zabiullah Mujahid said in an e-mail that the two helicopters were shot down and 36 soldiers died, but ISAF said there were no reports of enemy activity in the area where the crashes occurred.
A third ISAF service member died Monday in an insurgent attack in southern Afghanistan, the coalition said in a news release. No further details were released on the attack or the crashes.
After the first crash, those on board the chopper were taken to a NATO facility for evaluation. The crash did not harm civilians or damage property, ISAF said.
Some previous helicopter crashes involving ISAF members were the result of enemy fire, while others were for mechanical reasons.
The single deadliest loss for U.S. troops since the Afghan war began in late 2001 happened in August. Thirty U.S. service members died when a helicopter carrying them went down while they were reinforcing other troops, officials said. Seven Afghan troops died as well.
A U.S. military official said then that insurgents were believed to have shot down the CH-47 Chinook. The Taliban said that militants downed the helicopter with a rocket-propelled grenade.
More recently, 12 people died in March when a helicopter crashed in Afghanistan's capital city, Kabul. And in April, the Taliban claimed responsibility for downing a Black Hawk helicopter in southern Afghanistan.
The roadside bombing Monday struck a car in northern Baghlan province. All seven in the car died, police said.
The Taliban claimed responsibility in a text message from Mujahid. The police were targeted, he said.