KABUL - The Taliban have a sophisticated system in place to infiltrate Afghanistan’s security forces and vetting of recruits must be severely tightened, an Afghan army general said on Saturday.Infiltration has come under sharper focus because of a string of fatal attacks by Afghan security forces on U.S. soldiers since the burning of copies of the Muslim holy book at a NATO base last month ignited widespread protests.“Placing the rogues inside the army is well-planned by the enemies. The Taliban give them special training,” General Abdul Hameed, top army commander for the southern region of Afghanistan, told Reuters by telephone.“We must enhance intelligence gathering on the movements of recruits, tap their cellphones and we must find out who they are in contact with outside the army.”Two U.S. soldiers were shot and killed on Thursday in an attack involving at least one Afghan believed to be a soldier and a civilian, Western and Afghan officials said.The killings at a base in Kandahar in southern Afghanistan came less than a week after two senior U.S. officers were gunned down in the Afghan Interior Ministry by what Afghan security officials say was a police intelligence officer.About 70 members of the NATO-led force were killed in 42 insider attacks from May 2007 through the end of January this year. These attacks have become more frequent as the United States has sent tens of thousands of more soldiers to Afghanistan as part of a surge to fight in Taliban strongholds.Some of these incidents have been carried out by Afghan security forces reacting to the recent Koran burning, some have been due to private grievances and others have been carried out by Taliban insurgents who infiltrated the security forces. The killings in the Interior Ministry stunned NATO and cast doubt on its strategy of replacing large combat units with advisers as it tries to wind down the war, now in its 11th year. The Taliban claimed responsibility for the double murder but there has been no independent confirmation of that. Such attacks cast doubt on the effectiveness of Afghan government forces, which will be tasked with taking over security in one of the world’s most unstable countries once foreign combat troops head home at the end of 2014.The Taliban have proven remarkably resilient in the face of far superior Western firepower. But poor management of the recruiting process for the army and police has also given them an opportunity to infiltrate. “One of the reasons enemies infiltrated inside the army is because they are not properly identified when they are enrolled,” said Hameed. “The procedure is that new recruits must present birth certificate or any other documents to prove their identity but many present fake documents or don’t have any.” A Ministry of Defence official said the large size of the Afghan army and police — about 250,000 — made it difficult to stop infiltration. Afghanistan hopes to create a force of about 350,000 and then trim some of it.“We have identified and detained a number of suspicious soldiers recently who planned to carry out such (insider) attacks,” said Hameed.