The Irish Army conducted a controlled explosion of a pipe bomb discovered in a tote bag on board a bus heading for the capital, according to police officials.
The bus was traveling from Ballina to Dublin. Nearly 30 passengers left the bus during a search after a tip by an informant.
Despite the explosives, the queen continued her efforts to cement relations between Ireland and Britain that historically have been marked with war dating from the 12th-century invasion by King Henry II of England.
The queen laid a wreath at the Garden of Remembrance, recognizing those who fought against the Crown for Irish freedom.
Elizabeth is the first reigning monarch to visit the country since the founding of the Irish Free State in 1922.
“It was an extraordinary moment in Irish history,” British Prime Minister David Cameron told reporters.
