BERLIN - Arsonists attacked a refugee shelter in the southern German state of Bavaria, police said on Friday, as authorities struggle to cope with the biggest influx of people fleeing violence and poverty in the nation's post-war history.On Thursday, 17 people were injured in a riot in a refugee shelter in central Germany over a torn Koran and politicians have warned of growing tensions with the number of asylum-seekers and refugees expected to quadruple this year.Firefighters were able to get the fire at the refuge in Neustadt an der Waldnaab quickly under control after a resident alerted authorities to the fire there at 3.20 a.m. (0120 GMT), a police spokesman said.The 19 residents, who included three children, were not injured and all returned to the former guesthouse which is being used to house asylum-seekers.There were 150 arson or other attacks that damaged or destroyed refugee shelters in the first six months of the year.