Dempsey and other U.S. officials have remarked extensively in recent weeks on the need to improve the screening of Afghan recruits and to take other precautionary measures in the face of a series of attacks that so far this year have killed at least 51 allied troops, mostly of them Americans.
"But we've got to make sure our Afghan counterparts are as seized about it as we are," Dempsey said. "We have to get on top of this. It is a very serious threat to the campaign."
Dempsey commented after attending a meeting in Romania of NATO military representatives. He said they discussed the situation in Afghanistan, including plans for the remaining two years of the campaign and the insider attack problem.
In the latest instances of such attacks, two British soldiers were killed by an Afghan policeman in the southern province of Helmand on Saturday and four American troops were killed in a similar attack Sunday in Zabul province.
Dempsey said an assault on Camp Bastion, a British air base in Helmand province, on Friday in which two U.S. Marines were killed and six U.S. Harrier fighter jets were destroyed, should not be categorized as an insider attack even though the attackers were wearing U.S. Army uniforms.
He said an initial review of the matter had determined that the attackers had no inside assistance at Bastion. Other officials said the attack was clearly a well-planned, well-rehearsed assault carried out by Taliban fighters.
It was not immediately clear how the attackers got the U.S. uniforms or how they managed to do such extensive damage at Bastion