Afghan leaders appear ready to take decisive action to curb unprecedented "insider attacks" by Afghan recruits that have killed 40 Western troops this year, the top US military officer said Monday.

"For the first time, I found that my Afghan counterparts are as concerned about the insider attacks as we are," General Martin Dempsey, chairman of the US Joint Chiefs of Staff, said after talks in Kabul.

"In the past, it's been us pushing on them to make sure that they do more," he told AFP and Fox News.

The four-star general met commanders of the NATO-led force and Afghan top brass amid a surge in assaults by Afghan security personnel on their international colleagues.

A total of 10 soldiers, mostly Americans, have lost their lives at the hands of their Afghan allies in the past two weeks, and the attacks have caused almost one in every four coalition deaths in the war so far this month.

The 40 deaths so far this year amount to 13 percent of all international coalition fatalities in 2012.

The assaults have confounded the international force, which has touted its partnership with Afghan troops as the key to withdrawing combat troops over the next two years.

President Barack Obama, who spoke to Dempsey by phone, said Monday the United States was watching the rise in insider attacks with "deep concern", telling a White House news conference: "Obviously, we have to do more."

NATO and American officers have suggested the Afghan government has failed to come to grips with the problem but Dempsey said he came away "reassured" after discussions with his Afghan counterpart, General Shir Mohammad Karimi.

"I am reassured that the Afghan leaders, military and civilian, understand how important this moment is," Dempsey said.

Taliban insurgents have taken credit for the so-called green-on-blue assaults while NATO officers say an internal review showed only about 10 percent of them were the result of infiltration.

NATO has blamed the incidents on a mixture of cultural differences, personal vendettas and propaganda by Islamist militants.

In the latest incident an Afghan in police uniform killed a NATO soldier in the south on Sunday, shortly before Dempsey arrived, the military said.

The attacks are unprecedented in US military history and they have spawned so much mistrust that foreign troops have been ordered to be armed at all times, even within bases, officers said.

"I think there's no doubt it's a strategic threat," said one senior officer, who spoke on condition of anonymity.

Afghan authorities have adopted more rigorous vetting of recruits and NATO has bolstered counter-intelligence but the measures have failed to stem the problem.

NATO has about 130,000 soldiers fighting an insurgency by Taliban Islamists, but they are due to pull out in 2014 and now work increasingly with the Afghans they are training to take over.

Dempsey, on the first leg of a trip to Afghanistan and Iraq, said the insider violence would not alter the timetable for withdrawal or the coalition's emphasis on cooperating with Afghan recruits.

But the growing number of attacks is likely to add to pressure in NATO nations for an early exit from the increasingly unpopular conflict, now nearly 11 years old and America's longest war.

New Zealand pledged Monday to withdraw from Afghanistan as quickly as possible after three of its troops were killed, albeit in a bomb attack and not by their Afghan colleagues.

The insider attacks are on a scale unknown in recent wars such as those in Vietnam and Iraq, experts say.

Dempsey said the attacks were a new phenomenon for American forces but were not without precedent in Afghanistan, where British troops experienced similar assaults in the 19th century.

To deter the attacks, the coalition force might need to expand its partnership rather than scale back its cooperation with Afghans, he said.

Dempsey said it was possible that "the actual key to this would not be to pull back and isolate ourselves but reach out and embrace them even more."

There have been 32 insider attacks in 2012, killing 40 and wounding 69 coalition troops. For all of 2011, there were 16 attacks, leaving 28 dead and 43 wounded, according to NATO.