(CNN) -- NATO says the majority of attacks by Afghan security forces against coalition troops are driven primarily by personal grievances rather than an infiltration by insurgents.
"Some 10% we know are related to the insurgency," Brig. Gen. Gunter Katz, a spokesman for the NATO-led International Security Assistance Force, said late Friday.
The news follows word that U.S. Marine Gen. John Allen, commander of NATO troops in Afghanistan, ordered all troops in the country to carry loaded weapons around the clock following a spate of attacks by people wearing Afghan security uniforms, a U.S. official with direct knowledge of the order told CNN.
Allen's order, made in recent days, was divulged amid two more so-called green-on-blue or insider attacks Friday.
There have been a record 31 such attacks this year that have resulted in the deaths of 39 NATO service members, according to a report Friday on NATO's official online video channel.
The British Ministry of Defence, meanwhile, said Saturday that a British soldier was killed "by enemy action" Friday while on sentry duty in Helmand province in the south.
The death was not related to a green-on-blue attack, said Maj. Martyn Crighton, an ISAF spokesman. He did not release details about the attack or the nationality of the service member killed.
Troops in Afghan combat situations have always been armed, while only security forces have been regularly armed at the headquarters bases.
Under Allen's order, troops regardless of their tasks will now carry loaded weapons, said the official, who spoke on condition of anonymity.
While Katz did not comment on Allen's order, he said ISAF was taking steps to mitigate such attacks.
"Where there is an insurgency, there is going to be an attempt to infiltrate. You can't stop it. But what you can try to do is neutralize it," said Maj. Gen. James Ferron, a deputy commanding general.
Ferron, who oversees NATO's training of Afghan forces, said NATO was trying to not only put a stop to the attacks, but also the conditions that give rise to such assaults.
The attacks come at a critical time for the United States and NATO, which has picked up the pace of training Afghan forces even as it prepares to withdraw its combat troops by the end of 2014.
Violence continued to wrack the country Saturday, with a report that insurgents targeted a bridge being used by people on their way to shop at a bazaar in advance of Eid celebrations that mark the end of the Muslim holy month of Ramadan.
Four were killed and 11 wounded Saturday when a bomb exploded in the Shindand district in Afghanistan's western Heart province, a spokesman for the provincial governor said.
Masoud Popalzai reported from Kabul and Chelsea J. Carter reported from Atlanta. CNN's Ben Brumfield, Joe Sterling and Barbara Starr contributed to this report.