U.S. troops in Afghanistan have been ordered to significantly scale back operations with Afghan military and police forces after a spike in fratricidal “insider attacks” that has seriously undermined U.S. trust in their local allies.

The decision, officials said Tuesday, is also linked to concerns that American field troops have become more vulnerable to attacks because of Muslim outrage over a controversial anti-Islam video.

The orders from Gen. John R. Allen, the top U.S. and NATO commander in Afghanistan, represent a major shift from the long-stated U.S. philosophy that American and NATO troops are here to work “shoulder to shoulder” with their Afghan partners.

The fundamental U.S. strategy is to prepare some 350,000 Afghan forces to take over the country’s security by the end of 2014 so that the United States can pull out its combat troops.

Defense Secretary Leon E. Panetta said he was concerned by the ongoing treacherous attacks by Afghan forces on their U.S. and NATO counterparts, in which 51 foreign troops have died so far this year. But he downplayed suggestions that the U.S. strategy for withdrawing from Afghanistan would be hampered by the decision by U.S. commanders to sharply limit training and joint operations.

“We are concerned with regards to these inside attacks and the impact they are having on our forces,” Panetta told reporters in Beijing after meeting with Gen. Liang Guanglie, China’s defense minister.

“I rely on General Allen to take the steps that he believes are necessary to protect our forces, and at the same time I remain convinced that General Allen will continue to pursue efforts to implement the plan he has put in place so that we can complete the transition to Afghan security and governance and complete our drawdown by the end of 2014.”

The U.S.-led International Security Assistance Force said in a statement Tuesday that “most partnering and advising” would now be done at the battalion level and above. Lower-level joint operations will be “evaluated on a case-by-case basis” and must be approved by regional commanders.

As the morale-sapping insider attacks on the troops have escalated over the past two months, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, on Sunday described them as “a very serious threat” to the war effort.

Over the weekend, six international troops — four Americans and two Britons — died after Afghan forces opened fire on them, bringing the death toll in such attacks to 109 since 2007, when the phenomenon began. The shootings are also called “green on blue” to reflect the military’s designation of Afghan government forces as green and foreign allied forces as blue.

Although military officials have said it is too soon to tell whether the inflammatory “Innocence of Muslims” video has sparked an increase in shootings, an earlier statement from the coalition pointed to the video as one impetus for the new orders.

“Recent events outside of and inside Afghanistan related to the ‘Innocence of Muslims’ video, plus the conduct of recent insider attacks, have given cause for ISAF troops to exercise increased vigilance and carefully review all activities and interactions with the local population,” the coalition said.

It called the suspension of joint patrols and other ground-level activities “prudent but necessary.”

Allen on Sunday ordered commanders “to review force protection and tactical activities,” the Pentagon said. NATO spokesmen here have said Afghan leaders recommended the orders.

The orders are the second measure aimed at reducing insider attacks. U.S. Special Forces, which partners with local police in towns and villages, suspended training of 1,000 police recruits pending a new vetting of the existing 16,000- member forces.

Although the attacks have caused friction between U.S. and Afghan troops, Panetta said they were not an indication that the Taliban was gaining momentum in the war.

“I don’t think that these attacks indicate that the Taliban is stronger,” he said. “I think what it indicates is that they’re resorting to efforts that try to strike at our forces, try to create chaos, but do not in any way result in their regaining territory.”

In many parts of the country, all U.S. troops had been told to work only in partnership with Afghan forces, meaning there were no independent U.S. operations, just those with the Afghans in the lead and the Americans supporting them.

By suspending the integration of smaller units such as squads, platoons and companies, NATO is likely to create logistical and other problems for Afghan forces, said one Afghan general in southern Helmand province.

“It will be really difficult for us to conduct any operation without the NATO troops’ presence on the ground because we really need them,” said the general, who asked to be identified only by his last name, Malok.

He said field decisions now have to go through a coordination center that relays requests up the ranks, precipitating delays.

“Last week, our forces got killed and wounded in a land mine explosion ... and we urgently needed NATO’s help. I had to contact the coordination center first, and it took three hours for the medical evacuation helicopters to bring the soldiers to the hospital. It used to take them only one hour.”

But Gen. Abdul Raziq, a brigade commander in southwestern Logar province, said he supports the decision.

“Even if they are not with us on the ground, we do have their air support,” Raziq said. Because of that overhead firepower, he said, his current operation against the Taliban “is going very well.”

Some U.S. troops in the field complained over the weekend when the original guidance trickled down and some joint operations were abruptly halted.

In Wardak province, a restive area south of Kabul, for example, some commanders postponed several major operations for three days. Afghan army commanders in Wardak decided not to patrol without support from U.S. troops and canceled planned missions.

The decision to extend the pause in Wardak province’s Jaghato District to a third day came after some American and Afghan troops had already left on a pre-dawn operation Saturday. Afghan troops were given the option of continuing on the patrol into the enemy strongholds without U.S. support, but instead chose to return to their base.

“We look really bad to the Afghans right now,” said one platoon sergeant on the aborted patrol. “We are supposed to be supporting them, and we left them. This was a step backwards.”

Afghan soldiers and police in western Wardak were equally befuddled by the sudden U.S. decision to pull back.

“What happened with the [expletive] mission?” Jaghato District Police Chief Wahid Tanha asked his American counterparts after they had returned to their base Saturday morning. “Why didn’t you want to go?”

“You don’t understand. We wanted to go,” Sgt. 1st Class Christopher Naylor responded. “Our higher headquarters told us to come back.”

The Afghan police chief, speaking in broken English, reiterated his confusion about the canceled mission.

“You not want to go,” he insisted.

Greg Jaffe reported from Jaghato, Afghanistan. Craig Whitlock reported from Beijing.