LONDON (AFP) - A small bomb exploded in a Northern Ireland bank Saturday but caused no injuries, one day after Britain's Queen Elizabeth II ended an historic trip across the border in the Irish Republic. The blast in a shopping district of Londonderry also comes ahead of US President Barack Obama's visit to Ireland on Monday and amid a recent surge in unrest in British-ruled Northern Ireland blamed on dissident republicans. "There has been an explosion in the Shipquay Street area ... There are no reports of any injuries," a police statement said. A police spokesman told AFP: "We believe it was a sort of device". The targeted area of the city of Londonderry, close to the border with Ireland, had been evacuated following a warning. Police said it was not a controlled explosion. A second alert after the blast turned out to be a hoax. The incident comes after the queen on Friday ended a four-day trip to the Republic of Ireland aimed at reconciliation following the peace established in Northern Ireland as a result of the 1998 Good Friday accord. Protestant politicians who favour union with Britain united with Catholic republicans in condemning the bomb, which had been left inside a branch of the Spanish-owned bank Santander. Northern Ireland First Minister Peter Robinson of the Democratic Unionist Party, said the people of the province had made it clear in elections in early May that they did not want to return to the "dark days of the past." "This bomb was deliberately placed in one of the busiest areas of the city and was designed to murder innocent people as they shopped on a Saturday afternoon," he said. "The perpetrators of this disgusting attack have no regard for human life." Reports quoting local sources said the device was left on the floor of the bank by two masked men who then fled. Deputy First Minister Martin McGuinness of the republican Sinn Fein party and a former leading member of the Irish Republican Army (IRA), said those behind the blast had no mandate. "Those who carried it out need to realise that such an attack only hardens our resolve to ensure that peace survives and continues to flourish," he said. Queen Elizabeth's state visit to Ireland this week was surrounded by a massive security operation amid threats from dissident republicans opposed to any British presence on Irish soil. Ahead of her trip -- the first by a British monarch since the Republic of Ireland gained independence in 1922 -- police had received a coded bomb threat for London from Irish republicans. A bomb was also found on a bus near Dublin hours before her arrival. During the visit, the queen expressed regret and "deep sympathy" to the victims of Britain and Ireland's turbulent shared history in a speech seen as setting a new tone in relations between the two countries. Across the border in Northern Ireland, peace has held up relatively well since the 1998 peace accords signed between Catholics and Protestants which ended three decades of violence. But the province was rocked last month after a Catholic Northern Ireland policeman was killed in a car bomb attack. Meanwhile on Saturday, Ireland was preparing to welcome US President Barack Obama to one of his ancestral homelands. The US leader is making a 24-hour trip to Ireland on Monday and is set to make a speech to tens of thousands in Dublin's College Green road, where one of his Democratic predecessors Bill Clinton gave an address in 1995.