Gambian opposition leader Ousainou Darboe has said that he will seek legal advice on whether to challenge the outcome of Friday's elections.
Ousainou Darboe said the election was a "sham"
He said he rejected the official results, giving incumbent President Yahya Jammeh 67% of the vote.
Mr Darboe said there had been widespread intimidation by local chiefs, governors and security agents.
Mr Jammeh, meanwhile, dismissed critics of his human rights record, saying: "The whole world can go to hell."
Journalists and opposition activists have been threatened and harassed in recent years but Mr Jammeh was unrepentant after winning his third election, since taking power in a 1994 coup.
"If I want to ban any newspaper, I will, with good reason," he said, reports Reuters news agency.
"This is Africa and this is the Gambia, a country where we have very strong African moral values... If you write Yahya is a thief, you should be ready to prove it in a court of law. If that constitutes lack of press freedom, then I don't care."
The president, 41, also denied that security agents were involved in the 2004 killing of newspaper editor Deyda Hydara.
"I don't believe in killing people. I believe in locking you up for the rest of your life," Mr Jammeh said.
"Then maybe at some point we say: 'Oh, he is too old to be fed by the state,' we release him and let him become destitute."
Mr Darboe secured 27% of the vote, while another sociologist Halifa Sallah received 6%, according to official results.
"This election was just a sham. It was not free and fair and we don't accept the results as valid," Mr Darboe said.
He said he was considering his next move.
Voter turnout was about 59%, lower than in Gambia's last presidential election.
Due to a high level of illiteracy, voters used marbles to vote rather than ballot papers, inserting a marble into the drum representing their candidate.
Some 670,000 Gambians are registered to vote out of a population of 1.6 million.
Voting day was brought forward from October so as not to coincide with the Muslim holy month of Ramadan.