The rapid-fire spread of rumors has been problematic for the American-led mission in the past, particularly at times when insider attacks were high, and the spread of social media has only worsened the problem.

“Spreading the rumor that this was done by Resolute Support is throwing water into the enemy’s mill,” Mr. Abdullah told a meeting in front of news media cameras, referring to the name of the American-led NATO mission. “The killers of General Raziq are spreading these rumors.”

The attack in Kandahar has only furthered growing concerns among American military officials over whether proper protection measures are in place. The concerns have escalated at a time when the coalition mission, including about 15,000 Americans, is expected to provide more help to Afghan forces struggling against a resurgent Taliban.

The Czech Republic has contributed about 250 soldiers to the NATO mission in Afghanistan. Three Czech soldiers were killed in a suicide bombing near Bagram Air Base in August. Last week, a Czech vehicle was hit by a roadside bomb near the same base, wounding three soldiers, one severely, according an American military officer.

Following an insider attack in the southern province of Uruzgan in July, a Pentagon investigation looked at whether the Security Force Assistance Brigade, a small mobile advisory mission, had used proper security procedures. While troops in the country have added more personnel for protection following the attack in Uruzgan, and another in Logar, some are still wary about protocols that allow Afghan troops on American bases without any screening.

Two military officers said high-ranking American officers can allow specific Afghan soldiers onto some bases without body scans or checks of their names against an official database of known insurgents and accomplices.

While those Afghans might be personally vetted by the American officers in an attempt to build trust, the practice has left security personnel nervous about the increasing possibility of an insider attack.