U.S. and coalition commanders are no closer to knowing how deep the Taliban has penetrated Afghanistan’s security forces despite increased efforts to flush out infiltrators who are carrying out attacks against Americans.

“As for what percentage of the insider threat is related to infiltration or radicalization, I mean, it’s really difficult to determine,” Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey said Thursday.

“I’m sure a certain percentage of it is. And we’re treating it … as a threat,” he told reporters during a briefing at the Pentagon.