(Adds detail on foiled Canadian plot in paragraph 3, quote from NETF advisory in paragraph 6, and detail on bomb-detection equipment in paragraph 15)
By Richard Valdmanis
BOSTON, July 2 (Reuters) - Security will be tighter than ever in several U.S. cities during Independence Day celebrations this week, which will see some of the largest public gatherings in the country since the deadly Boston Marathon bombings in April.
Security officials said they would deploy record numbers of police and install scores of new surveillance cameras and checkpoints around fireworks displays, concerts and other Fourth of July events in Boston, New York, Washington and Atlanta.
A foiled al Qaeda-inspired plot to detonate bombs in Canada's Pacific coast city of Victoria during Monday's Canada Day holiday - Canada's equivalent to U.S. Independence Day - has underscored the security concerns.
"The increase (in security) is, of course, related to the Marathon bombing and other global events," said David Procopio, a spokesman for the Massachusetts State Police, noting that Boston's Independence Day events were reportedly the Boston Marathon bombers' initial target.
The National Explosives Task Force (NETF) meanwhile said it has urged fireworks sellers in the U.S. to report buyers who raise suspicion. The Boston bombers used materials from fireworks to build their bombs, as had a man convicted of attempting to bomb New York's Times Square in 2010.
The NETF said in an industry advisory that fireworks sellers should look out for people with "injuries consistent with experimentation with explosives such as missing hand/fingers" or who are "making suspicious comments regarding radical theology, anti-U.S. sentiment."
Three people were killed and 264 injured when two pressure-cooker bombs loaded with shrapnel and fireworks-grade gunpowder exploded at the finish line of the Boston Marathon April 15, in the biggest attack on American soil since the Sept. 11, 2001 attack on New York's World Trade Center towers.
Tamerlan and Dzhokhar Tsarnaev, the two brothers suspected of carrying out the attack on the marathon, had originally planned to set off their homemade bombs on July 4, but attacked earlier because they had made the devices sooner than expected, law enforcement officials have said.
Boston's Independence Day events include concerts and a fireworks display along the city's waterfront that traditionally attracts a half million people.
A federal indictment says Tamerlan - who was killed in a shootout with police days after the bombing - purchased 48 mortars containing some eight pounds of low-explosive powder from a fireworks store in New Hampshire in February.
Dzhokhar is in jail awaiting trial on charges including murder and using a weapon of mass destruction. He could face the death penalty if convicted.
Massachusetts State Police Commissioner Timothy Alben said the state will deploy record numbers of uniformed and undercover cops, install a 'significant' number of new surveillance cameras, boost boat patrols, and ban items like backpacks and large coolers at the events.
"Please be assured that the steps ... are not the result of any specific threat to these events. We have no intelligence of any such threat," he said.
Massachusetts officials have declined to provide additional details of the security measures, but said they were the result of collaboration with other police departments with counter-terrorism experience, including those in New York and London.
U.S. laboratory equipment company Thermo Fisher Scientific said it has loaned half a million dollars worth of handheld devices to Massachusetts police during the Independence Day events in Boston to help officers quickly identify chemicals that might be used in bombs.
Police officials in New York and Washington also said they were tightening security.
"Coverage includes large numbers of uniformed and plain clothes police officers, police helicopters and boats, additional mobile cameras, radiation detection, and street checkpoints," said Paul Browne, Deputy Commissioner of the New York City Police Department.
In Atlanta, where there will be a Fourth of July fireworks display and an annual Peachtree Road Race, officials said the entire police force would be working, and surveillance along the race course would be increased.
"There should not be a single spot on the route that does not have camera coverage," Atlanta Police Chief George Turner said. "The specter of what happened in Boston with the marathon on April 15 weighs heavily on our hearts and minds." (Additional reporting by Svea Herbst-Bayliss in Boston, Edith Honan in New York, David Beasley in Atlanta, and Ian Simpson in Washington; Writing by Richard Valdmanis; Editing by Barbara Goldberg, Bernadette Baum and Bernard Orr)