NAIROBI, Kenya — Major election complications cropped up on the Tanzanian island of Zanzibar on Wednesday, and the main opposition party on the mainland called for a recount as Tanzania’s election limbo stretched into its third day.

Observers had predicted that Sunday’s elections would be the closest and possibly most troubled in Tanzania’s history. Tanzania is considered one of the most peaceful nations in Africa, led by essentially the same political party since independence more than 50 years ago.

But many Tanzanians are growing tired of that party, and already there have been worrisome signs. Ballot papers were burned by a mob in western Tanzania on Sunday. On Monday, opposition officials said scores of their volunteers were arrested.

And on Wednesday, officials on Zanzibar, a semiautonomous island with miles of soft, white sand, suddenly declared election results from all local races void. The opposition had seemed poised to sweep those races, and though the decision to hold new local elections does not affect the nationwide presidential tally, observers said it was sure to raise already percolating tensions.