Giuliani happened to be in London, in a hotel near the city's Liverpool station, about a block from where one of the bombs went off.
Giuliani says the resolve shown by Londoners in resuming their normal lives Friday was remarkable: "They are very, very strong people. You can never really understand something like this. Innocent people being killed by these cowards. It's a horrible thing. It is horrible for them and their families. Our hearts go out to them.
"But the reaction of the people of London is exactly right. You don't let these cowards affect you. You move forward, you go about your life.
"When I was watching them yesterday, and I spent a lot of time watching them, I was reminded of the fact that these are the descendants, pretty direct descendants, children, grandchildren of the people who got through the Battle of Britain in 1940. And you could see that.
"You could see these are very strong people. These people are not going to let these terrorists affect them. They're going to move forward."
Giuliani added there are lessons to be learned from the London blasts.
"They'd experienced I.R.A. terrorism. This is the most experienced police and emergency force in dealing with terrorism. What it demonstrates is you never have a foolproof plan.
"We have to be 100 percent accurate and correct all the time. All they need is one little opening, one little place where there isn't surveillance. And in a city as big as London or New York or Chicago or Washington or whatever, that's always possible.
"The thing that I can say is their emergency response … seemed to me to be absolutely first-rate. I mean, they were right on it. Their firefighters and police officers handled it perfectly. I'm sure they're going to go back now and try to figure out why they didn't find out about it in advance, and maybe they'll plug up a few more holes."