During a visit to the U.S. city of Boston, British Prime Minister David Cameron said democracies "should never give in to terrorists" and should tackle the spreading of extremist propaganda.
On May 14, Cameron visited the site of the Boston Marathon bombings.
He said "the narrative" of the fundamentalists must be countered in order to prevent the radicalization of young Muslims.
Cameron and Massachusetts Governor Deval Patrick visited a makeshift memorial in the city's Copley Square.
The April 15 explosions at the marathon's finish line killed three people and injured more than 260.
One suspect, 26-year-old ethnic Chechen Tamerlan Tsarnaev, died after a shootout with police days later, while a second suspect, his 19-year-old brother Dzhokhar, is in a federal prison hospital.
Cameron met with President Barack Obama at the White House on May 13.
Based on reporting by AP and SkyNews