Four men have been arrested after a bomb was found in Londonderry.
Police said the viable device was discovered after officers investigating dissident republican activity stopped a car in the Westway area of Creggan last night.
The discovery comes ahead of a visit by US Secretary of State Hillary Clinton, who will speak at Stormont and visit the new Titanic Centre later on Friday.
Clinton's husband Bill was a crucial part of the Northern Ireland peace process in 1998.
Two men aged 47 and 49 were arrested at the scene at about 8.40pm.
Two others, also in their 40s, were arrested later.
A spokeswoman for the Police Service of Northern Ireland said: "All four have been taken to Antrim Serious Crime Suite and are assisting police with their inquiries."
A number of homes had to be evacuated as Army bomb disposal experts made the bomb, described as a viable improvised explosive device, safe.
SDLP Foyle MLA Pat Ramsey said people in Derry were angry at the disruption caused by the bomb.
He said: "Once again the people of Creggan are the victims of disruption, distress and anger. There is a palpable sense of anger - and relief that nobody was hurt. It could have been much worse."
Tensions in Northern Ireland have been high in recent days after a controversial vote on flying the Union flag over Belfast City
Loyalists have been staging protests across the country to show their opposition to the decision to restrict the number of days the flag is flown.
Councillors from the non-sectarian Alliance Party have been intimidated and in one case party offices in Carrickfergus were destroyed by fire.