By Rob Taylor
KABUL (Reuters) - A rogue Afghan soldier shot dead two U.S. troops in east Afghanistan on Monday, the NATO-led coalition said, the latest in a series of insider killings that have strained trust between the allies ahead of a 2014 pullout by foreign combat troops.
The deaths in Laghman province brought to 12 the number of foreign soldiers killed this month, prompting NATO to increase security against insider attacks, including requiring soldiers to carry loaded weapons at all times on base.
They also come a week after U.S. Joint Chiefs of Staff chairman Martin Dempsey visited Kabul to talk about rogue shootings and urge Afghan officials to take tougher preventative action.
"ISAF troops returned fire, killing the ANA (Afghan National Army) soldier who committed the attack," the NATO-led International Security Assistance Force said in a statement.
There have been 33 insider attacks so far this year that have led to 42 coalition deaths. That is a sharp increase from 2011, when, during the whole year, 35 coalition troops were killed in such attacks, 24 of whom were American.
Afghanistan's government said on Wednesday it would re-examine the files of 350,000 soldiers and police to help curb rogue shootings of NATO personnel, but accused "foreign spies" of instigating the attacks.
The killings, many of which have been claimed by the Taliban as evidence of insurgent reach and infiltration, have eroded trust between the NATO-Afghan allies and are complicating plans for transition to Afghan security within two years.
NATO commanders have played down the threat of infiltration, blaming most of the shootings on stress or personal differences between Afghans and their Western advisers that ended at the point of a gun, a frequent occurrence in Afghanistan.
But the U.S. general leading NATO forces in Afghanistan acknowledged last Thursday that the Taliban could be traced to more insider attacks than previously acknowledged, accounting for about a quarter of the cases.
The Afghan government agreed after Dempsey's visit to improve the vetting of army and police recruits by requiring stronger guarantors, a more stringent test questionnaire and biometric data on all would-be and existing personnel.
More undercover intelligence officers would be recruited and placed in Afghan security forces to keep an eye on soldiers and police, while security force members with families in neighboring countries would be heavily scrutinized for possible relations or exposure to cross-border insurgents.
But President Hamid Karzai's spokesman also said the number of attacks was also relatively small given the presence of 120,000 foreign troops among 350,000 Afghan security forces.
Taliban insurgents on Sunday killed 10 Afghan soldiers and wounded four in an attack on a checkpoint in volatile southern Helmand province, provincial officials said.
(Reporting by Rob Taylor; Editing by Nick Macfie)