The way a child behaves has a lot to do with the way they percieve their surroundings.  If they are feeling insecure, anxious, or not in control of their environment they are much more likely to show that through negative behaviors because they are not yet able to appropriately explain it using their words.  
 
Moving alone can cause anxiety in a child.  Add in that the fact that the move was to a different country and that your child is dealing with autism, and it's very understandable that their behavior has gotten worse.  Children with autism have increased difficulty expressing emotions appropriately, so your child may be acting out because they don't know how else to express their anxiety about the move.  Try to explain as best you can to your child what is happening so they don't feel like they are surprised by any upcoming events.  Kids that feel like their life has changed drastically will often cling to any familiarity they can find.  Keep familiar pictures and objects around the new flat.  Do your best to keep a daily routine, and if possible integrate your schedule from the old house into your new one.  Kids respond well when they know what's expected of them.  Require your son to do the same chores and have the same responsibilities as they did in the old house.  If your son is feeling anxious about the move, use lots of encouragement and praise for his positive behaviors.  Let him know that you are there for him no matter what and even though the surroundings have changed, your love for him has not!  
 
Best of Luck, Boys Town National Hotline 1-800-448-3000