KABUL (Reuters) - Three U.S. soldiers have been shot dead by an Afghan worker on a military base in southern Afghanistan, in a deadly 24 hours for NATO-led forces in the country during which six soldiers died in rogue attacks. The shooting took place on Friday night in the Garmsir district of Helmand province, not far from where three U.S. special forces soldiers were killed by an Afghan policeman and comrades earlier in the day. ...