The reports that US soldiers accused of plotting and then killing innocent civilians in Afghanistan smoked hashish have sparked concerns among US military officials about how often other US troops may use illegal drugs as well.

Hashish is plentiful and easy to obtain in Afghanistan, and its use has long been a source of concern for US military officials trying to gauge the performance of Afghan soldiers and police.

But those officials are now increasingly discussing whether hashish use is also spreading among American soldiers in Afghanistan or whether the current case is an aberration.

“Certainly that kind of problem is a huge issue if it’s out there,” Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said Wednesday at a Monitor-sponsored breakfast for reporters.

But he took issue with the notion that use of hashish is on the rise among US troops. “I just – I haven’t seen it. And I don’t mean that it hasn’t just been reported. I haven’t seen any kind of significant rise in the data, the kind of testing we do to test people – test all our troops with respect to drug use – that would indicate that.”

Precisely what constitutes a “significant rise” remains an open question. For now, Mullen said that he is satisfied with the drug-testing requirements that the Defense Department has in place for troops.

In the wake of these reports, US officials also continue to grapple with ongoing concerns about the extent to which US commanders in the unit were aware of or could have prevented the troubling crimes that US troops are accused of committing.

While Mullen declined to comment directly on the case of soldiers in the 5-2 Stryker brigade, which in July was reflagged the 2nd brigade of the 2nd infantry division, he emphasized the importance of command responsibility in the military. “Fundamental to command in every service is accountability,” he said. “It’s the responsibility we give you and it’s accountability as a leader.”

In the US Navy tradition, ship captains face serious questions if their vessels run into a buoy, for example. “It’s how I was obviously raised in the Navy and having commanded at a lot of levels,” he added, “I feel very strongly about it."