The United States on Tuesday declared  an urgent imposition of visa restrictions on some Nigerians it alleged of trying to undermine democracy at this year’s general elections.

The ban, which the State Department described as specifically targeted towards certain individuals, came about five months after Nigerians went to the polls in presidential, senatorial and state elections.

“These individuals have operated with impunity at the expense of the Nigerian people and undermined democratic principles and human rights,” Morgan Ortagus, a spokesperson for the State Department, said in a statement.

The statement did not name the individuals or say how many were affected by the measure. President Muhammadu Buhari was declared winner of the February 23 election, which was marred by postponements, logistical challenges and violence.

A former State Department official said U.S. privacy regulations prohibit the government from naming the individuals affected by the restrictions.

The results of the presidential election were challenged by the main opposition leader, Atiku Abubakar. Mr Abubakar and his Peoples Democratic Party (PDP) said election officials had connived with Mr Buhari’s party to tamper with results, an allegation strongly denied at the ongoing election petitions proceeding.

The State Department did not comment on the election results but said it had identified specific persons who employed sinister tactics to sabotage democratic principles and human rights.

The U.S. was amongst several countries that threatened to impose sanctions on any individual suspected of fomenting violence or any acts that did not conform with democratic norms.

The U.S. ambassador to Nigeria, Stuart Symington, also encouraged citizens to disobey illegal directives that might be issued in the name of the president during the election.

The warnings came amidst widespread pre-election fears powered by controversial statements of politicians. One of such comments came from Kaduna State Governor Nasir El-Rufai.