Two U.S. service members were among five killed Sunday when a British helicopter crashed in Afghanistan's capital, Kabul, the third mass-casualty event involving transport aircraft in the war-torn country in three months, coalition forces in Afghanistan said Monday.

The other dead were two British service members and a French civilian contractor in what the NATO-led military mission described as a "non-hostile incident." The crash involving a British Puma Mk 2 helicopter happened at 4:15 p.m. local time at Camp Resolute Support in Kabul, and an investigation is underway.

"We're deeply saddened by the loss of our teammates," U.S. Brig. Gen. Wilson Shoffner, military communications chief in Afghanistan, said. "Our heartfelt condolences go out to the families and friends of those affected in this tragic incident and we pray for the full recovery of the injured."

An Afghan security guard who witnessed Sunday's crash told The Associated Press the helicopter struck a monitoring balloon as it was landing. "It seemed like the cable was turned around the helicopter rotor," the security guard, Najibullah, said. Like many in Afghanistan, he goes by one name. He said the helicopter went down and then black smoke rose from the area.

A second helicopter circled the area three or four times and then landed at a nearby airport, he said.

In London, the Ministry of Defence also said a convoy of British military vehicles came under attack earlier Sunday in a separate incident in Kabul, but there were no fatalities.

Gen. Abdul Rahman Rahimi, Kabul's police chief, said an explosion targeted a NATO military convoy in Kabul, wounding three civilians. He said the blast targeted two armored vehicles attached to the NATO Resolute Support mission, damaging one of them. He did not specify whether the vehicles were British.

While Rahimi and a Taliban spokesman said the convoy was attacked by a suicide car bomber, U.S. Army Col. Brian Tribus, the spokesman in Afghanistan for U.S. and NATO forces, said it was a roadside bomb. The discrepancy could not immediately be reconciled.

The Interior Ministry said in a statement that the three civilians suffered minor wounds. It said the blast damaged surrounding buildings.

Taliban spokesman Zabihullah Mujahid sent a statement to local media claiming responsibility.

There have been a number of attacks in the capital in recent weeks, including one on Oct. 6 targeting the house of former Helmand governor Nahim Baloch. After an all-night battle, 10 people were wounded, including three civilians and seven members of the Afghan security forces. Officials said Baloch was not at home at the time.

The Taliban have been active across the country this year, most recently storming the northern city of Kunduz and holding it for three days before largely retreating in the face of a government counteroffensive.