Helicopter crashes killed 14 Americans on Monday in the deadliest day for the U.S. mission in Afghanistan in more than four years. The deaths came as President Barack Obama prepared to meet his national security team for a sixth full-scale conference on the future of the troubled war.

In the first crash, a helicopter went down in the west of the country after leaving the scene of a firefight with insurgents, killing 10 Americans — seven troops and three civilians working for the government. Eleven American troops, one U.S. civilian and 14 Afghans were also injured.

In a separate incident, two U.S. Marine helicopters — one UH-1 and an AH-1 Cobra — collided in flight before sunrise over the southern province of Helmand, killing four American troops and wounding two more, Marine spokesman Capt. Bill Pelletier said.