<p><br /> A gunman has shot dead two American soldiers and seriously injured two people on a US Army bus at Frankfurt airport.<br /> </p><p><br /> The gunman is believed to be from Kosovo.<br /> </p><p><br /> Security around the airport has been tightened and an investigation is under way.<br /> </p><p><br /> German Chancellor Angela Merkel, speaking in Berlin, confirmed the deaths.<br /> </p><p><br /> "We don't know the details but I would like to express how upset I am. We have to do everything we can to find out what happened," she told a news conference.<br /> </p>
