US Secretary of Defence James Mattis. Photograph:( Reuters )
Insider attacks are often known as 'green on blue' attacks in which Afghan service members or attackers wearing Afghan uniforms fire on US or coalition troops.
US Defense Secretary Jim Mattis, who recently visited Kabul, said on Tuesday that the Afghan government was increasing the vetting and training of local forces in order to minimise so-called insider attacks.
A US service member was killed in an apparent insider attack in eastern Afghanistan earlier this month and a member of a US army training unit was shot dead by an Afghan soldier in the southern province of Uruzgan in July.
Mattis visited Kabul last week and met with Afghan President Ashraf Ghani, who brought up the issue of insider attacks.
"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 radicalised," Mattis told reporters at the Pentagon.
"There's a lot of attention from their military side that's actually in the field with the troops and by attention, I mean training of their people and how they protect the coalition troops," Mattis added.
Insider attacks, often known as “green on blue” attacks in which Afghan service members or attackers wearing Afghan uniforms fire on US or coalition troops, have been a regular feature of the conflict in Afghanistan, although their frequency has diminished in recent years.
Coalition forces have in the past tightened security and added extra force protection measures including special “Guardian Angel” units to accompany training units.
Mattis also said that the United States was getting mixed messages from Taliban militants and while they were increasing violence in some parts of the country, they had also shown more of an interest in reconciliation.
"I think there is a fair amount of what I would call non-quantifiable factors that are mounting in terms of going in the right direction," Mattis said.
A suicide bomber in Afghanistan killed at least 32 people and wounded more than 120 at a demonstration on Tuesday on the highway between the eastern city of Jalalabad and the main border crossing into neighbouring Pakistan.
Violence has flared across the nation, with heavy fighting in northern provinces, and officials have said it is likely to intensify before parliamentary elections next month and a presidential election in April.