KANDAHAR (AFP) - A US soldier on Thursday shot dead an Afghan police officer in the southern city of Kandahar, prompting an immediate investigation, the US military said. A US soldier has shot and killed an Afghan National Police officer in Kandahar. An investigation is ongoing as to the cause, a US military statement said, giving no further details. US troops are helping to train Afghan police with a view to them taking over responsibility for security and allowing foreign forces to withdraw. Some 136,000 Afghan army soldiers and nearly 120,000 police have been trained so far as part of the NATO mission, with a goal of nearly 172,000 soldiers and 134,000 police by November next year. Publicly coalition soldiers say local police and army are making progress but some say privately that relations have been strained by several incidents in which rogue Afghan police and soldiers have shot dead foreign troops.