The U.S. State Department said on Tuesday it had imposed visa restrictions on Nigerians it said were involved in trying to undermine democracy in presidential and parliamentary elections this year.The department did not name the individuals or say how many were affected by the visa restrictions.President Muhammadu Buhari won a second term in February in an election marred by delays, logistical glitches and violence."These individuals have operated with impunity at the expense of the Nigerian people and undermined democratic principles and human rights," spokeswoman Morgan Ortagus said in a statement."The Department of State emphasizes that the actions announced today are specific to certain individuals and not directed at the Nigerian people or the newly elected government," Ortagus added.