LAHAINA, Hawaii (Reuters) - Pacific trade talks are unlikely to end in a deal due to an impasse over trade in autos and dairy goods and monopoly periods for biologic drugs, sources close to the negotiations said on Friday.

Three sources involved in the talks said although ministers from the 12 countries negotiating the Trans-Pacific Partnership were due to meet again shortly, a deal was improbable.

"It would be very difficult to arrive at a deal," one of the officials said, requesting anonymity because discussions were ongoing.

(Reporting by Krista Hughes and Ami Miyazaki; Editing by Ken Wills)