Vice President Yemi Osinbajo - who is acting as head of the country while Buhari is on holiday, ordered the dismissal of DSS chief Lawal Musa Daura "with immediate effect".
Sources said the handing over to Seiyefa was being conducted at the Yellow House headquarters of the agency by the agency's director of administration and logistics as Daura was not available at the ceremony.
Seiyefa hails from Bayelsa State.
He also attended the University of Jos, where he obtained a Bachelor of Law (Honours) Degree in 1982, and was called to bar after attending the Nigeria Law School, Victoria Island Lagos.
Said: "The Nigeria Police Force wishes to categorically state that its personnel was not involved in any way whatsoever in the blockade of the National Assembly in the early hours of today, 7th August, 2018".
Saudi Arabia orders all of its foreign university students to leave Canada
Canada has said it is "gravely concerned" about the arrests and has called for those detained to be released immediately. Riyadh on Sunday recalled its ambassador from Canada and gave the Canadian ambassador to Saudi Arabia 24 hours to leave.
Idris returned to the Villa around 6.35p.m for another round f meeting with the acting president.
A senior aide to Senate President Bukola Saraki was among a number of people who tweeted pictures and video from outside the National Assembly building.
Acting President Yemi Osinbajo has met with the newly appointed acting director-general of the Department of State Services (DSS), Matthew Seiyefa at the Presidential Villa, Abuja. "Seiyefa is also a member of the National Institute".
A Reuters witness said security agents, some of whom were masked, then allowed lawmakers to enter but continued to bar government agents and journalists.
Acting President, Yemi Osinbajo has described as a gross violation of the law, the blockage of the National Assembly by security operatives from the Department of State Services, (DSS) and the Police.