Irish republican politician Gerry Adams was denied entry to the White House’s St. Patrick’s Day celebration Tuesday due to reported “security” and administrative reasons.

Adams, the leader of Ireland’s Sinn Fein party, was made to wait outside the event for 80 minutes before he decided to leave. Adams said that he received his “usual” invitation to the White House event, but once he arrived at a security checkpoint, he was told there was a security issue preventing him from entering. Adams released a statement after leaving the event, saying he “will not sit at the back of the bus for anyone.”

“After two decades of travelling back and forth to the USA and countless meetings in the White House with successive U.S. presidents, this is an unacceptable development,” said Adams. “It is obvious that there remain some within the US administration who seek to treat Sinn Féin differently.”

Though Adams was not allowed into the event, his deputy, Mary Lou McDonald, and Sinn Fein’s Northern Ireland Deputy First Minister Martin McGuinness were given entry.

Adams has been a notable figure in Irish republican politics for several decades. His rise in Sinn Fein began in the late 1970s and continued through some of the most violent years known as “the Troubles,” a period that saw violent conflict between those who wanted to unite Northern Ireland with the rest of the country and those who were British loyalists.

The Sinn Fein party operates in both Ireland and Northern Ireland and seeks an independent and united Ireland. It has often been associated with the Provisional Irish Republican Army (PIRA), an off-shoot of the original IRA that fought for Irish independence during the revolution from 1919 to 1921.

The PIRA fought a guerrilla war with British and loyalist forces from the 1960s to 1998 after a non-violent Catholic civil rights campaign in Northern Ireland was met with violence from loyalist government forces. PIRA is a listed organization under the U.K’s Terrorism Act 2000 and considered an unlawful organization under Ireland’s Offenses Against The State acts, though officially the group is not referred to as a terrorist group by neither Ireland nor the U.S.

Adams has been accused of being a member of the PIRA, but he has denied the allegations and maintained that he is only a Sinn Fein politician.

The U.S. Secret Service issued a statement after the event saying it regretted the handling of the situation. “Unfortunately, an administrative input error received by the Secret Service was not able to be rectified promptly,” said the statement.

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