The US Secret Service has expressed regret for a delay admitting Sinn Féin President Gerry Adams to an event at the White House last night.

In a statement issued to RTÉ News tonight, a Secret Service spokesman said: "The Secret Service would like to express our regret that the issue involving Mr Gerry Adams’ entry into the St Patrick’s Day reception could not be resolved in a more timely manner.  

"Unfortunately, an administrative input error received by the Secret Service was not able to be rectified promptly."

Mr Adams earlier said he was unacceptably delayed when trying to enter the event and called on US authorities to explain the delay. 

He said he had attended the event on numerous occasions and had been invited by US President Barack Obama.

Earlier in the day Mr Adams had attended the Speaker's Lunch, which was also attended by President Obama.

When he arrived at the White House event, staff informed him that there was an issue of "security", Mr Adams said. 

After encountering a long delay, Mr Adams decided to leave.

He said the treatment was not good manners as he was an invited guest, and somewhere there was a list and he was on that list.

He added that the incident followed the treatment of Sinn Féin representatives at airports en route when they were also subject to special searches.

Mr Adams said: "It is obvious that there remain some within the US administration who seek to treat Sinn Féin differently."

He added that he, Martin McGuinness and Mary Lou McDonald had met with some members of Congress today who had shared their grave disappointment at the situation.

He said: "Sinn Féin will not sit at the back of the bus for anyone. We are elected to represent citizens and we will do this."