U.S. President Barack Obama said he is concerned about the "green on blue" attacks, the recent killings of NATO troops by Afghan security forces.
At a news conference Monday, Obama said he has spoken to senior military leaders who are in Afghanistan talking to coalition and afghan counterparts about the recent "uptick" of such incidents.
Afghan security forces have killed 10 international troops, mostly Americans, in the past two weeks. In the latest incident Sunday, a person wearing an Afghan police uniform shot and killed a coalition service member. At least 39 international coalition members have been killed in such attacks this year.
Also Monday, top US military officials cited progress in the campaign against insurgents in Afghanistan.
The chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, and the commander of U.S. Central Command, General James Mattis arrived in Afghanistan for talks with NATO and Afghan officials.
NATO said the two commanders met with the head of U.S. and NATO forces in Afghanistan, General John Allen, and discussed "how to maintain momentum against the insurgents" and building Afghan capacity. The discussion focused on recent "insider" attacks.
NATO troops have been ordered to carry loaded weapons at all times, even when on their bases, as a precaution against the attacks.
The Taliban said it has infiltrated the ranks of Afghan security forces and considers the attacks a major part of its strategy against alliance forces.
General Dempsey and General Mattis are also meeting with other senior Afghan and coalition leaders on Monday.
U.S. Defense Secretary Leon Panetta discussed the issue of insider attacks with Afghan President Hamid Karzai in a phone call Sunday. The Defense Department said Panetta urged Karzai to boost counterintelligence cooperation with NATO, introduce more rigorous vetting of Afghan security recruits and engage in more dialogue with village elders who can vouch for such recruits.
The Pentagon said Karzai and Panetta agreed that U.S. and Afghan officials should work more closely together to minimize the potential for future attacks.
Also Monday, New Zealand's prime minister, John Key, said his country's forces will likely complete their withdrawal from Afghanistan by April of next year, roughly six months earlier than originally planned.
Mr. Key said the move is not prompted by the deaths this month of five New Zealand soldiers, including three on Sunday in a roadside bombing in central Bamiyan province.
The province's governor, Habiba Sarabi, told VOA's Afghan Service Monday that Afghan forces will fill any security gaps left by the departure of international troops.