KABUL (AP) — Four American troops were killed and two injured Monday when two helicopters collided in southern Afghanistan.

Hostile fire has been ruled out in the crash, a military statement said. U.S. military spokesman Col. Wayne Shanks said he did not have other details yet about the cause of the collision.

Shanks said the injured had been evacuated to hospitals inside Afghanistan.

In an unrelated incident, another helicopter went down Monday during an operation by international forces against insurgents in western Afghanistan in which a dozen militants were killed.

The U.S. said military casualties were reported and a recovery operation is under way. Casualties could refer to either dead or injured.

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.

So far in October, more than 30 American troops have died.

The deaths come as U.S. officials debate whether to send tens of thousands more troops to the country and the Afghan government scrambles to organize a runoff election between President Hamid Karzai and his top challenger from an August vote that was sullied by massive ballot-rigging.

President Barack Obama’s administration is hoping the runoff will produce a legitimate government. Another flawed election would cast doubt on the wisdom of sending more troops to support a weak government tainted by fraud.

Some Obama administration officials had said the U.S. would be receptive to a deal to avoid another disruptive election if Karzai and Abdullah agreed.

On Sunday, Karzai and his rival, former Foreign Minister Abdullah Abdullah, both ruled out a power-sharing deal before the Nov. 7 runoff, saying the second round of balloting must be held as planned to bolster democracy in this war-ravaged country.

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