British police said Monday that they received a bomb threat to central London, a day before Queen Elizabeth II’s historic visit to Ireland and a week before President Obama’s state visit to Britain. 

Early Tuesday morning, police carried out a controlled explosion of a bomb found in the luggage compartment of a bus traveling on the outskirts of Maynooth in County Kildare west of Dublin. A second suspected bomb turned out to be a hoax, wire reports from Ireland said.

The threat is thought to be linked to dissident Irish Republicans who oppose the peace process in Northern Ireland. Several streets around Buckingham Palace in central London were cordoned off Monday morning. Images on television showed a police officer strapped in a harness emerging from a manhole, reportedly checking sewers after the manhole was discovered ajar. 

“A bomb threat warning has been received relating to central London today. The threat is not specific in relation to location or time,” Scotland Yard said in a statement.

“We believe it’s connected to dissident Irish Republican terrorism,” a Scotland Yard spokeswoman said, speaking on the condition of anonymity as is police policy.

The spokeswoman also confirmed there were two security alerts in the British capital Monday morning, but she stressed that such alerts occur frequently. In one case, bomb disposal experts carried out a controlled explosion of an abandoned suitcase that turned out not to be a threat, she said.

In its statement, Scotland Yard urged Londoners to “go about their business as usual,” while reporting “unusual activity or behavior which may be terrorist-related” to the police.

On Tuesday, Queen Elizabeth II will become the first British monarch to visit the Republic of Ireland since 1911. The Irish Embassy in London said that more than 8,000 police officers and 2,000 troops are being deployed in Ireland for the monarch’s visit, the largest security operation in the republic’s history.

Despite the bomb warning Monday, Scotland Yard said there has not been a change in terrorism-related threat levels. The overall threat level in Britain from international terrorism is “severe,” the second highest of five possible ratings. The threat level from Irish-related terrorism is “substantial,” the third highest rating and remains unchanged since it was raised in September 2010.

Adam is a special correspondent.