By Hamid Shalizi and Jack Kimball
KABUL (Reuters) - While NATO soldiers worry whether an Afghan partner might turn from an ally to a lethal foe, Afghan soldier Sayed Rahim says he's afraid his own comrades at a small outpost in eastern Paktika province will kill him.
"There are some soldiers who have Taliban war songs on their cellphones," Rahim said. "Do we do our duty, or should we watch out for these guys who will kill us one day?"
While successive attacks by rogue Afghan security forces against NATO allies worry Western commanders, less-known incidents of Afghan-on-Afghan violence within the security forces point to Taliban infiltration nearer to home.
More than a decade since coalition forces toppled the Taliban, NATO forces and the Western-backed government are scrambling to build up local security forces ahead of the withdrawal of most foreign combat troops by the end of 2014.
The surge in attacks by lone Afghan security force members on NATO troops has raised concern over the ability of Afghan soldiers and police to take primary responsibility against the tenacious insurgency in the two-and-a-half years still left.
Insider attacks have killed 17 NATO soldiers this year, forcing the coalition to take new steps to safeguard troops working with Afghans, including "guardian angel" protectors.
Personal grievances, battle stress, and domestic problems are behind more attacks than Taliban sympathies, according to NATO forces, who put the number of incidents by Islamic militant infiltrators this year in single digits.
The NATO coalition says a similar number of Afghan troops and police have died at the hands of their own compatriots.
"I can't really sleep. Soldiers don't trust one another very much. When I go to sleep I fear someone will shoot me dead," said Rahmatullah, a comrade of Rahim's near the Pakistan border, through which insurgents cross with reinforcements and material.
"We are also very fearful of food and night guards but what can we do? We are soldiers and have to do the job," the 24-year-old said in a province where an Afghan policeman this month drugged nine colleagues and shot them dead as they slept.
"EXTREME ATTEMPT TO INFILTRATE"
In a country with myriad ethnic and political divisions, many Afghan officials have turned to close relatives or tribesmen to protect them as infiltration worries mount.
"They feel safer with their relatives or tribesmen around them for security, not with strange faces. But we make sure to properly train them," one security source said, declining to be named because of security sensitivities.
"The officials believe their own men won't target them. It's their choice."
But even shielding by close family or ethnic allies does not always keep them safe.
In July last year, Afghan President Hamid Karzai's younger half-brother, one of the most powerful men in southern Afghanistan, was killed at home by a highly-trusted bodyguard.
The highly-contested and divided political loyalties within one of the world's poorest countries are set to intensify as national elections near in 2014 with no clear successor for Karzai, who is constitutionally barred from another term.
Add the withdrawal of foreign troops the same year and the volatile country could slide into another cycle of bloodletting.
Key to avoiding more bloodshed will be the transition from coalition forces to Afghan security personnel who NATO hopes will be ready to wrest control over regions of the country where major insurgent groups continue to wage attacks.
But the large size of the Afghan army and police, now at about 250,000, makes it difficult to stop infiltration.
Afghan counter-intelligence agents are being placed into police and army units while there are more regular checks of biometric data taken on all Afghan security personnel against that of Taliban militants or supporters.
"There's an extreme attempt by the enemy to infiltrate us," an Afghan security official told Reuters.
Police have already cracked down in Herat province, where 70 officers were arrested for corruption, criminal activity or ties to the Taliban. The program is expected to be rolled out to other provinces over the next year, the security official said.
Tensions between Afghans and Western forces have also ratcheted up after the killing of 17 Afghan villagers for which a U.S. soldier has been charged and the burning of copies of the Muslim holy book at a NATO base.
"Foreign soldiers are very suspicious of us and they think anyone from us will kill them," soldier Rahim in Paktika said.
"It's the fault of the government and foreigners because they let anyone in but don't care where the new recruits come from and whether they have something to do with Taliban."
(Additional reporting by Kamal Khan in Khost; Editing by Rob Taylor & Kim Coghill)