It follows Saturday's election which led to the re-election of President Muhammadu Buhari for a second four-year term.
The 76-year-old defeated his main rival, former Vice-President Atiku Abubakar, with a margin of nearly four million votes.
Mr Buhari got 15.2 million votes while Mr Abubakar received 11.3 million.
Mr Abubakar's People's Democratic Party (PDP) has rejected the result.
Turnout was a record low at just 35.6% and Mr Abubakar, 72, said this was the result of a deliberate policy to prevent his supporters from voting.
President Muhammadu Buhari insisted the election had been fair.
Dr Khataza Gondwe is Sub-Saharan Africa officer for Christian Solidarity Worldwide. She told Premier's News Hour there has been some questioning of the election result:
"In November, a key influencer in Nigeria said that the number of registered voters was slightly inflated, so he actually pointed to the fact that this may not be the cleanest of elections."
She said videos had shown thugs seizing ballot boxes and setting them on fire, mass printing of ballot papers and intimidation by the army at some voting stations in the south of the country.
Delays and violence marred the run-up to Saturday's poll but no independent observer has cited electoral fraud.
In the 1980s, Mr Buhari was one of several military rulers in Nigeria and this election marks the 20th anniversary of the return to civilian rule.
Christian Solidarity Worldwide said it is concerned that not enough has been done to stop attacks on Christians in the country.
Dr Gondwe told Premier what the government now needs to do:
"To protect citizens from every form of attack, whether it comes from this militia, which has to be addressed, or Boko Haram or these gangsters and thugs and kidnappers who are roaming the country and just terrorising the people in their own homes."
You can listen to the full interview with Dr Khataza Gondwe here:
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