Story highlights Secret Service blames the mix-up on an administrative error

"It is obvious that there remain some within the US administration who seek to treat Sinn Fein differently," Adams says

(CNN) The Secret Service apologized Wednesday for denying Sinn Fein leader Gerry Adams entry to a White House reception, blaming the mix-up on an administrative error.

Adams was invited to attend St. Patrick's Day celebrations on Tuesday.

When Adams arrived, he says staff informed him that there was an issue of security.

"After two decades of travelling back and forth to the USA and countless meetings in the White House with successive US Presidents, this is an unacceptable development," Adams wrote in a statement. "It is obvious that there remain some within the US administration who seek to treat Sinn Fein differently."

Adams is a prominent Catholic politician who helped broker peace in Northern Ireland and who has long been associated with the Irish Republican Army, which had ties to Sinn Fein. Today, Sinn Fein is an opposition party in the Republic of Ireland and is the second-largest party in Northern Ireland's Legislature.

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