uznemiriti

1. to upset; to alarm; to worry
   Njegovo pismo me je jako uznemirilo. — His letter really upset me.
   Vest o zemljotresu uznemirila je građane. — The news of the earthquake alarmed residents.
2. to disturb; to bother
   Tiho, nemoj da uznemiriš bebu. — Quiet, don't disturb the baby.
3. (uznemiriti se) to get worried; to become alarmed
   Uznemirila se kad joj se sin nije javio. — She got worried when her son didn't call.

The polite formula uses the imperfective: "Izvinite što vas uznemiravam" (sorry to bother you).