"We're to the point now where we can't trust these people," a senior military official told NBC News
"It's had a major impact on our ability to conduct combat operations with them, and we're going to have to back off to a certain degree," the official said.
The suspensions are indefinite and "could last three days or three months," another official told NBC.
Six NATO troops were killed in Sunday's attack at a remote checkpoint near a NATO installation in southern Zabul province, including the four Americans, and 51 NATO troops have been killed this year in so-called blue-on-green attacks either by Afghan forces or insurgents posing in uniforms as Afghan police or security forces, NBC said.
In a similar insider attack last weekend, two British soldiers were killed in southern Helmand province by an Afghan believed to a member of the local police.
Also Sunday, at least eight women reportedly died during NATO airstrikes in mountainous regions in eastern Afghanistan, local officials said. The civilian deaths were condemned by Afghan President Hamid Karzai.
On Friday, the Taliban launched a daring attack on the heavily fortified Camp Bastion base in Helmand province, killing two Marines and damaging or destroying eight attack jets with damage estimated at more than $200 million, The New York Times reported, quoting military officials.
The incident has raised concern among military officials as the extremely well-defended facility was reportedly attacked by three teams in U.S. Army uniforms.
"We're saying it's a very sophisticated attack," a military official told the Times. "We've lost aircraft in battle but nothing like this."
Helmand has been a bastion province of the Taliban, who have escalated their violence as U.S. forces plan to end combat operations in Afghanistan by 2014, allowing Afghan forces to take control of their country.
Military officials were trying to determine if the insurgents who attacked Bastion received help from inside and whether they received training in Pakistan or Iran, the Times said.
One insurgent was captured and 14 others killed in the attack. Besides the two Marines killed, no coalition personnel were injured.
Britain's Prince Harry, doing a tour of duty as a helicopter pilot, was stationed at Camp Bastion at the time of the attack, but was not hurt, the Times said.
The Post report said the weekend incidents involving the insider attacks and the civilian deaths would raise more mistrust among NATO forces, while creating more alienation against them among Afghans.
It wasn't known if the weekend insider attacks were in any way related to the protests in Middle East over an anti-Islam film.
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