The Afghan military has increased its vetting of local forces working with U.S. troops in order to minimize insider attacks, Defense Secretary Jim Mattis has said.
Mattis told reporters at the Pentagon on September 11 that Afghan President Ashraf Ghani brought up the issue when the two met in Kabul last week.
Insider attacks, in which members of Afghan security forces or assailants dressed in Afghan uniforms fire on coalition troops, have become less common in recent years but remain a persistent worry.
A September 3 attack that killed one U.S. soldier and wounded another in eastern Afghanistan was carried out by a member of the Afghan National Police.
It came nearly two months after a member of a U.S. Army training unit was shot dead by an Afghan soldier in the southern province of Oruzgan.
Mattis said that Afghan leaders had increased security checks and training of local forces to make certain they are identifying any Afghans who have been radicalized.
"There's increased vetting going on...they are bringing in more people that we have helped train to know how to do it, to make certain we're catching people who have been radicalized," he said.
Around 14,000 U.S. troops are currently stationed in Afghanistan, where the Western-backed government in Kabul has been struggling to fend off the Taliban and other militant groups.
On September 11, Afghan officials said at least 32 people were killed and around 130 wounded in a suicide attack on a gathering of protesters in the eastern province of Nangarhar.
There was no immediate claim of responsibility.