UPDATE 1 — Swedish parliament speaker asks opposition leader to explore government formation

(Adds quote, detail in paragraphs 3-5) STOCKHOLM, Sept 18 (Reuters) — The speaker of Sweden's parliament Andreas Norlen said on Friday he has asked opposition leader Magdalena Andersson of the Social Democrats to explore the formation of a new government following Sunday's centre-left election victory. Swedish Prime Minister Ulf Kristersson of the right-wing Moderates on Thursday announced his resignation following the narrow loss for his four-party bloc. Andersson earlier on Friday said she was ready to begin the work on forming a government. "She has told me that she is ready to take on this task," Norlen told a press conference. Andersson faces a difficult mission of uniting Sweden's four centre-left political parties, some of which have said they do not want to govern together or support a government they are not part of. (Reporting by Simon Johnson and Terje Solsvik, editing by Louise Rasmussen) ((anna.ringstrom@thomsonreuters.com)