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Massachusetts Gov. Deval Patrick, left, walks with British Prime Minister David Cameron through a corridor at the Statehouse in Boston. (Associated Press)

BOSTON -- British Prime Minister David Cameron visited an impromptu memorial that sprang up near the site of the Boston Marathon bombings, striking a combative tone Tuesday in saying that democratic and multiracial countries like the United States and Britain will never give in to terrorists who feed on "the poisonous narrative" of violence, extremism and victimhood.

Cameron was accompanied by Massachusetts Gov. Deval Patrick when he visited the makeshift memorial that includes T-shirts, letters, running shoes and other items in the city's Copley Square.

The United Kingdom, Cameron said, has experienced that sort of terrorism in London and elsewhere and knows to stand up and say terrorists will never win.

"Obviously, what we do for the future, we have to do everything we can to work with law enforcement agencies to maintain our vigilance," Cameron said after walking through the memorial amid tight security. "But, I think, above all, we have to say very loudly, very proudly, very clearly that we are proud to live in a country -- whether it is America or Britain -- that is a democracy, that loves freedom, that loves diversity, that is a multiracial country and we'll never give in to terrorists."

Cameron is in Boston to offer his condolences and discuss lessons that can be learned from the bombings.

"One of the things we have to do is we have to challenge the poisonous narrative on which they feed, a narrative of violence, extremism, victimhood," Cameron said.

The attacks sparked one of the biggest manhunts in Massachusetts, which ended days later when one bombing suspect died after a gunbattle with police and the other was arrested.

"It is hard to believe people can do these things to countries like ours when we are freedom-loving, when we are democracies, when we do value people's rights, but these things do happen and we have to fight them and challenge them. That's what I know you are going to do right here in Boston," Cameron said before leaving the site.