Kabul, Afghanistan ? A helicopter carrying NATO peacekeepers crashed in a western Afghan desert Tuesday and another flying with it made an emergency landing, killing 17 Spanish troops and injuring five others providing security ahead of landmark legislative elections.

There were conflicting reports about what caused the crash, the biggest loss of life for NATO forces in Afghanistan. A spokesman for NATO’s International Security Assistance Force said the crash and emergency landing in Herat province were believed to be accidents, but Spain’s defense minister said he did not rule out hostile fire.

“It could have been an accident or it could have been an attack from the exterior,” Jose Bono said in Madrid.

Afghan President Hamid Karzai said the crash was caused by a sandstorm.

However, Afghan army commander Abdul Wahab Walizada, whose troops provided security at the crash site, said the weather was fine. He said the helicopters were flying too close together, and the rotor blades of one clipped the other.

Andrew Elmes, spokesman for the International Security Assistance Force, speaks in a news briefing Tuesday in Kabul, Afghanistan after two transport helicopters carrying NATO peacekeepers crashed.

One helicopter burned while the other was damaged severely, he said.

The 17 dead – 12 soldiers and five crew – were on the chopper that crashed, ISAF spokesman Maj. Andrew Elmes said. The five injured were on the second, which made a “hard landing,” he said. They were in stable condition at an ISAF hospital in Herat.

Twelve other troops on the second chopper were not injured.

In Washington, Pentagon spokesman Bryan Whitman said preliminary information showed no indication the aircraft was shot down or collided with another craft.