KABUL (AP) — 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 in the south, two other U.S. choppers collided while in flight, killing four American troops and wounding two more, the military said.

It was the heaviest single-day loss of life since June 28, 2005, when 16 U.S. troops on a special forces helicopter died when their MH-47 Chinook helicopter was shot down by insurgents.

U.S. authorities have ruled out hostile fire in the collision but have not given a cause for the other fatal crash in the west. Taliban spokesman Qari Yusuf Ahmedi claimed Taliban fighters shot down a helicopter in northwest Badghis province’s Darabam district. It was impossible to verify the claim and unclear if he was referring to the same incident.

U.S. forces also reported the death of two other American troops a day earlier: one in a bomb attack in the east, and another who died of wounds sustained in an insurgent attack in the same region. The deaths bring to at least 46 the number of U.S. troops who have been killed in October.

This has been the deadliest year for international and U.S. forces since the 2001 invasion to oust the Taliban. Fighting spiked around the presidential vote in August, and 51 U.S. soldiers died that month — the deadliest for American forces in the eight-year war.

The Obama administration is debating whether to send tens of thousands more troops to the country, while the Afghan government is rushing to hold a Nov. 7 runoff election between President Hamid Karzai and challenger Abdullah Abdullah after it was determined that the August election depended on fraudulent votes.