German authorities are investigating 40 cases in which Islamic militants are suspected of having entered the country with the recent flood of refugees from the Middle East, the federal police said on Wednesday. That represents a doubling of such cases since January and is likely to deepen concerns about the threat level in Germany, which has not suffered a large-scale Islamist attack like those that have rocked neighbours France and Belgium in recent months. In the past, the German government has played down the risks of Islamic State fighters entering Europe with the tide of migrants, in part to avoid...