DERRY, Northern Ireland (CBS/RTV/ITN) -- Police in Northern Ireland discovered a home-made bomb in a car in Derry on Thursday night (December 6).
The device was found by officers investigating dissident republican activity.
Witnesses said police rammed the vehicle at around 2040gmt and found the home-made bomb, which has now been made safe.
Four militant nationalists have been arrested.
A few hours later police revealed they had also discovered a letter bomb in a loyalist area of Co Down.
U.S. Secretary of State Hillary Clinton visits Belfast on Friday (December 7) to lend her support to the British province's fragile peace, underlined by more overnight rioting and the bomb discoveries.
Making one of her last foreign trips as U.S. Secretary of State, she visits a province transformed by the 1998 peace agreement that her husband, former President Bill Clinton, helped bring about in what was regarded as one of the greatest successes of his presidency.
But Northern Ireland remains with sectarian tensions. The 1998 peace has mostly held, although militant nationalists have stepped up attacks in recent years.
As this week's violence has underlined, clashes involving nationalists, loyalists and police still break out in Belfast several times a year.