British army bomb experts made safe "a substantial amount" of home-made explosives, left under the Foyle bridge in Derry.
Security sources blamed the Real IRA for the incident. The Foyle bridge remains closed.
Earlier today, two pipe bombs were found in a GAA sports ground in Co Derry.
British Army bomb disposal experts were called to deal with the devices which were uncovered during a search of Desertmartin Gaelic Athletic ground near Magherafelt.
They were found near an entrance and by a perimeter fence.
Two other bombs were also defused in Garvagh and Gulladuff.
Loyalist paramilitaries issued a warning yesterday that GAA grounds in counties Derry and Tyrone would be targeted.
The dissident loyalist Red Hand Defenders issued a warning that it was planning to step up its terror campaign.
The group also claimed responsibility for a pipe bomb placed in the letterbox of Mr Martin McGuinness's Cookstown constituency office and a booby trap device under the van of a republican ex-prisoner in Armagh yesterday.