U.S. Defence Secretary Leon Panetta said Tuesday the U.S. is concerned about the impact insider attacks are having on its forces in Afghanistan.

But he insisted Gen. John Allen, the top U.S. commander there, is taking necessary steps to protect the force while still ensuring the U.S. will be able to hand over security to the Afghans and be able to withdraw by the end of 2014.

Panetta did not specifically address the dramatic action taken Monday by Allen, as NATO decided to temporarily scale back its operations with Afghan security forces in order to lower the risk of them turning their guns on American and allied forces.

Instead, he argued that the attacks do not mean the Taliban is getting stronger. "I think what it indicates is that they are 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 that has been lost," he told reporters during a press conference in Beijing with China's minister of national defence, Gen. Liang Guanglie.

Until now, U.S. and NATO troops routinely conducted operations with their Afghan counterparts. But under the new order, such operations for now will require the approval of a regional commander.

Escalating worries

NATO's decision reflected escalating worries about the insider attacks, coupled with the widespread tensions over an anti-Islam video that has prompted protests in Afghanistan and as many as 20 other countries around the world.

Panetta, however, has suggested that the insider attacks represent a risk of war that must not impede the overall goals.

U.S. Secretary of Defence Leon Panetta speaks at a news conference with China's Defense Minister Liang Guanglie (not seen) in Beijing Tuesday. (Larry Downing/Reuters)

"Every day when you are engaged in war, there are serious risks that confront those who fight the war," Panetta said Monday. "We will do all we can to minimize those risks but we will not lose sight of the fundamental mission here, which is to continue to proceed to assure a peaceful transition to Afghan security and governance."

In a separate statement issued after the press conference, Pentagon press secretary George Little said the changes in joint operations "will often be short notice and based to the latest information." And he said the operations will always be conducted "in a manner that mitigates risks to our troops and ensures mission success."

Early Tuesday, a suicide bomber rammed a car packed with explosives into a minibus carrying foreign aviation workers to the airport in the Afghan capital, Kabul, killing at least 12 people. The Islamist militant group Hizb-i-Islami claimed responsibility for the dawn attack, saying it was revenge for the anti-Islam video.

So far this year, 51 international troops have been killed by Afghan forces or militants wearing their uniforms. The attacks have spiked in recent months, damaging the trust between the NATO and Afghan forces at a time when ongoing training and co-operation are critical in order for allied troops to leave Afghanistan by the end of 2014 and turn control of security over to the Afghan forces.