Kabul, Afghanistan ? Afghan security forces shot and killed three international troops Monday, one of them an American, in two attacks. They were the latest in a rising number of attacks in which Afghan forces have turned their weapons on their foreign partners.

The killings reflect a rise in tensions between Afghan and international forces that follow an American soldier’s alleged massacre of Afghan civilians, the burning of Muslim holy books at a U.S. base, and uncertainty about Afghanistan’s fate as foreign troops prepare to pull out.

They also come at a time when international troops have stepped up training and mentoring of Afghan soldiers, police and government workers so that Afghans can take the lead and the foreign forces can go home. The success of that partnership is key to the U.S.-led coalition’s strategy to withdraw most foreign combat forces by the end of 2014.

U.S. Marine Gen. John Allen, the top commander of U.S. and NATO forces in Afghanistan, told reporters at the Pentagon that these types of attacks are characteristic of any warfare involving insurgents.

“We experienced these in Iraq. We experienced them in Vietnam,” Allen said. “On any occasion where you’re dealing with an insurgency and where you’re also growing an indigenous force … the enemy’s going to do all that they can to disrupt both the counterinsurgency operations” and the developing nation’s security forces.

Since 2007, an estimated 80 NATO service members were killed by Afghan security forces, according to an Associated Press tally, which is based on Pentagon figures released in February. More than 75 percent of the attacks have occurred in the past two years.