U.S. troop killed, "insider" escapes after latest attack in Afghanistan

Updated at 4:08 a.m. Eastern

(CBS/AP) KABUL, Afghanistan - Two men in Afghan police uniforms shot at U.S. troops in southern Afghanistan Sunday, killing one and injuring another, Afghan security officials tell CBS News..

ISAF, the international military coalition in Afghanistan, confirmed the latest "insider attack" took place in Spin Boldak, in Kandahar province, on Sunday evening, but would not confirm the nationalities of Western forces who came under attack.

Sunday's shooting brings to 32 the number of reported green-on-blue, or insider attacks in 2012. At least 40 coalition forces have been killed in such incidents this year, including 26 Americans.

At least ten Western forces have been killed in insider attacks in just two weeks.

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One of the attackers was killed on Sunday when ISAF troops returned fire, but the other escaped the scene, according to an ISAF spokesperson.

The surge in violence by Afghan allies against their international partners has raised doubts about the ability of the two forces to work together at a key transition time. Afghan forces are expected to take over security for the country by the end of 2014, when the majority of international combat forces are scheduled to leave.

The shooting comes just days after a statement released by the head of the Afghan Taliban, Mullah Omar, claiming that militants had successfully infiltrated Afghan security forces to carry out such attacks.

The Taliban often claim responsibility for green-on-blue attacks, which the U.S. military recently began referring to officially as "insider" incidents, but the Pentagon maintains the attacks are not generally not carried out by insurgents, but rather individual members of the Afghan security forces who may develop a grudge against their Western allies.

On Saturday, Defense Secretary Leon Panetta called Afghan President Hamid Karzai to encourage him to work with U.S. commanders to ensure more rigorous vetting of Afghan recruits.

On Friday it was disclosed that U.S. troops have been ordered to carry loaded weapons at all times in Afghanistan, even when they are on their bases, as a precaution against such attacks.

Panetta announced last week that new counter-intelligence measures had been adopted during the past year to try and prevent the green-on-blue attacks. While he acknowledged that some of the incidents have been connected to insurgent groups, he maintained that the vast majority appear to be carried out by individuals with no known links to, or coordination with, the Taliban or other militant organizations.

Even the Taliban leader conceded in his written statement that not all of the attacks were carried out by his militants, but he expressed his appreciation to the "conscious Afghans in the rank and files of the enemy," some of whom, he claimed, had gone on to "join the ranks of Mujahideen, carrying their heavy and light weapons and ammunition."

U.S. military officials say the majority of suspects in the insider incidents are killed or captured soon after they turn their weapons on their colleagues, but some have escaped, such as the suspect in Sunday's shooting.

In conjunction with Afghan commanders, the U.S. has used an eight-point vetting process to try and identify and exclude Afghan recruits who pose a threat, but neither Panetta nor other U.S. commanders have elaborated on what new steps are being taken, or can be taken, to confront the problem.

Standing now at 40, the number of international forces killed in green-on-blue attacks in 2012 has already surpassed the toll from all of 2011, when 35 Western forces were killed.

In central Afghanistan, meanwhile, three NATO service members were killed Sunday when a vehicle struck a roadside bomb, officials said. Bamiyan Gov. Habiba Sarabi said the blast went off in Kohmard district while the troops were out on patrol. Afghan security forces tell CBS News the troops were from New Zealand.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the attack in a statement.

Including Sunday's deaths, at least 41 international troops have been killed so far this month in Afghanistan.