Improvised explosive devices were found on a Dublin-bound bus and at a tram stop near Dublin hours before the British Queen was to land in the city, the first time in 100 years for a British monarch to visit the Republic of Ireland.

The Irish army carried out a controlled explosion to neutralize the bomb found in the luggage compartment of a bus on the outskirts of Maynooth, Co Kildare.

Another explosive device was discovered at a tram stop in Inchicore, in the outskirts of Dublin. The latest Dublin bomb scare came after a bomb threat gripped London in panic on Monday.

The queen and her husband, the Duke of Edinburgh, will arrive in Dublin on Tuesday in what will be the first visit by a British monarch to Ireland after the republic gained independence from Britain.

A multi-million-dollar security operation has been carried out in the run-up to the royal visit, especially in the backdrop of some opposition to the visit in Ireland.

I think 100 years on from the last time a British monarch visited Ireland I think there is a great sense of history and occasion, said British Prime Minister David Cameron, who will join the queen in the Irish tour.

On Monday life came to a halt in parts of London as police got a bomb threat. A bomb threat related to Central London has been received on Monday. The threat is not specific in relation to location or time, police said.