KABUL, Afghanistan – Insurgent attacks in Afghanistan during the past three months were up 11 percent, compared to the same period last year, according to the latest statistics on monthly violence released by the U.S.-led coalition.

The figures, which NATO released on Thursday, also show that the number of attacks in June was the highest for any month since fighting surged in the summer of 2010.

The disturbing uptick comes at a time when foreign troops are leaving and insurgents are trying to prove they remain a potent force. It also supports the theory that the insurgency remains undefeated after more than a decade of war, though coalition officials caution against using attack numbers as a bellwether of how the war is proceeding.

The number of “enemy-initiated attacks” – such as roadside bombings and gunfire attacks from insurgents – rose in all three months of the second quarter, compared with the same months in 2011. .

The coalition offered two possible reasons for the uptick. A shortened poppy harvesting season prompted insurgents to start their spring offensive earlier.

Also, with more Afghan security forces on the ground and taking the lead in more operations.