The Chechen brothers accused of the 2013 Boston attacks hailed from just a few hundred kilometres away from the Olympic sites at Sochi. This Black Sea town and neighbouring Caucasus Mountains are readying to host world leaders, thousands of athletes and many more spectators at the Feb. 7-23 games.
Twin bombings in another southern Russian city in December have heightened terrorism fears around the Sochi events.
Intelligence agencies from multiple countries will be working together around the clock at a special headquarters in Sochi, Putin said while visiting Olympic sites Wednesday.
"In the U.S., people died at a marathon, during the G-8 there were terrorist acts in the London subway," he said, according to Russian news agencies.
Putin rose to power and popularity 15 years ago on law-and-order, hard-on-terrorism policies that critics say go too far and suppress human rights. He had long warned the West about the dangers posed by Chechen rebels, and urged closer security co-operation with Washington after the Boston Marathon attacks.
Putin has made security central to the Olympic project, in which he has taken an unusual personal interest.
Despite hang-ups and criticism and higher costs than any Olympics in history, Putin told athletes and staff Wednesday that "Russia is ready to host the games."
The Olympic zone on the Black Sea shore still looks like a construction area. Some hotel rooms aren't quite finished. And electricity outages occasionally disrupt the intense security measures.
Putin obliquely referred to the unfinished nature of some sites, calling Sochi "the world's biggest construction project." The construction started largely from scratch, as workers filled in swamp land on the shores of the Black Sea for the skating arena, hockey stadium and other key sites, and built up ski facilities on what had been largely untapped slopes.
Putin proudly oversaw the raising of a Russian flag in front of Olympic venues, but didn't mention other criticism he and Russia have come under about the games: corruption in building projects, pressure on environmental activists, anger over a Russian law seen as infringing on gay rights, even a campaign to shoot stray dogs in Sochi's streets.
Humane Society International sent Putin a letter urging him to stop targeting the dogs. Calling it "not only inhuman but ineffective," the group in a statement recommended mass sterilization and vaccination instead.
Putin also gave a pep talk to Russia's Olympic athletes, after the national disgrace of winning just 15 medals in Vancouver in 2010.
Fans "will be watching your every appearance with the greatest attention," he is quoted as saying. "We are all counting on you."