Prime Minister Ulf Kristersson of Sweden expressed his increasing concern on Monday after another wave of gang violence over the weekend. “This weekend has been one of the worst we have seen in a very long time,” the conservative head of government told Swedish radio station SVT on Monday. Since violent crime did not stop by itself, far-reaching measures were needed to deal with gang crime, Kristersson said. Criminals must be locked up, he said, and those without Swedish citizenship must be deported. It will take time, however, to get a grip on the problem, he added, referring to the years of …