KABUL - Eleven US troops and three US drug enforcement officials were killed in two helicopter crashes in Afghanistan yesterday, the heaviest one-day loss for American forces in more than four years, military officials said.

The crashes involved three copters, two of which collided midair in the south of the country and a third that went down in the wake of a firefight in Afghanistan’s west, according to NATO and US officials.

Among the dead was Captain Kyle R. VanDeGiesen, 29, a Marine pilot from North Attleborough, Mass.

Hostile fire was ruled out in the midair collision, which killed four American troops and injured two others, but the cause of the other crash was not immediately determined.

The Taliban claimed to have shot down a Western helicopter yesterday in Afghanistan’s northwest, but it was not clear whether that was the same event the military described.

The firefight broke out after US and Afghan forces searched a compound believed to harbor drug traffickers, the military said. The drug trade is a major source of revenue for the Taliban and other insurgents, and pursuing traffickers has become part of the war effort for coalition forces.

The deaths of the three US drug agents marked the Drug Enforcement Administration’s first deaths since it began operations here in 2005.

The deaths comes as the Obama administration is weighing the request of its top commander, General Stanley A. McChrystal, for a substantial troop increase. President Obama and his security team held a sixth full-scale conference yesterday on the future of the war.

The loss of life and aircraft showed the extent to which Western forces in Afghanistan are dependent on helicopters. In much of the country, terrain is extremely rough, distances long, and roads all but impassable. Roadside bombs add to the danger of ground transport.

Weather did not appear to be a factor in either of the crashes.

A North Attleborough High School graduate whose wife is expecting their first son was one of 14 Americans killed in two helicopter crashes in Afghanistan yesterday, in one of the deadliest days for US forces since fighting began there eight years ago.

The family of Captain Kyle R. VanDeGiesen, 29, a Marine helicopter pilot, confirmed yesterday that he died in one of the crashes.

The family said they did not know what occurred and released a statement saying, “It is with sadness today that we learned that our son, brother, and husband, Marine Captain Kyle VanDeGiesen, was killed today in the line of duty in Afghanistan.’’

The statement continued, “He was a 1998 graduate of North Attleborough High School, a 2002 graduate of Saint Anselm College, and was currently stationed at Camp Pendleton in San Diego, Calif. He fulfilled his lifelong dream of becoming a Marine helicopter pilot, protecting his family and serving his country.’’

His wife, Megan, is expecting their first son soon, and the couple have a daughter, Avery, who celebrated her first birthday in the spring while her father was in Afghanistan.

VanDeGiesen also leaves his parents, Ruth Ann and Calvin VanDeGiesen; his brothers, Ryan and Christian; and his sister, Caitlin.

Funeral arrangements were pending.

VanDeGiesen was a star football quarterback, and became part of the first Saint Anselm College varsity football team in decades. He was a Boston Globe All-Scholastic in 1997.

But even in his days of sports, he had long talked of his plan to become a pilot, said Peter Cordella, chairman of the criminal justice department at Saint Anselm, who was his teacher and knew him through the football program.

He said VanDeGiesen was the type of student that faculty, staff, and students alike remember years after knowing him.

“There are some students who really stand out: You remember them; you wonder what they were doing,’’ said Cordella. “Clearly, he’s someone you remember. He had a sense of purpose. He knew exactly what he wanted to do, and what he wanted to do was go in the military and become a pilot. He knew that from Day One.’’

The military has released little information about yesterday’s crashes, except to say they were not a result of hostile fire.