The election commission said it moved the poll date because troops
needed to protect polling stations were being deployed to fight Boko
Haram.
The postponement was welcomed by the ruling party, but the US said it was "disappointed".
Attahiru Jega, head of the election commission, said the postponement
was necessary as he had been told that troops would not be available to
protect voters as they were too busy conducting operations against Boko
Haram.
"The commission cannot lightly wave off the advice of the nation's security chiefs," he said.
The chairman of the opposition All Progressives Congress (APC), John
Odigie-Oyegun, said the move to delay the elections until 28 March,
announced late on Saturday, was "highly provocative" and "a major
setback for Nigerian democracy".
However, he urged Nigerians to "remain calm and desist from violence and
any activity which will compound this unfortunate development".
Opposition officials accuse the military of forcing the electoral
commission into the delay to help the sitting president's campaign.
However, Attahiru Jega, head of the election commission, said
the postponement was necessary as he had been told that troops would
not be available to protect voters as they were too busy conducting
operations against Boko Haram.
"The commission cannot lightly wave off the advice of the nation's security chiefs," he said.