"I suspect there are more members of MI5 in Northern Ireland today than there are members of dissident republican movements," said Kevin Toolis, author of "Rebel Hearts," a study of the Provisional IRA.
Toolis doubted whether today's three principal factions — the Continuity IRA, Real IRA and Oglaigh na hEireann, Gaelic for "warriors of Ireland" — can attack England, given British surveillance and infiltration of their relatively puny ranks.
"It's clear that British Army intelligence and MI5 were very successful in penetrating the upper echelons of the (Provisional) IRA, and they've cracked the dissident groups too," Toolis said. "If there's three men in a room trying to organize an attack, they can't be confident one of them won't phone up their MI5 handlers five minutes later."
Tom Clonan, a security analyst and former Irish army captain, said IRA dissidents would see an Olympics-linked attack as a powerful way to embarrass Britain.
"The dissidents have already demonstrated they're mad and bad enough to want to target Britain," Clonan said. "If they end up doing nothing during the Olympics, or just phoning in threats with nothing real behind them, it would show that they're being surveilled within an inch of their life."
The U.K.'s Joint Terrorism Analysis Centre in London currently rates the likelihood of an attack in Britain by IRA splinter groups or al-Qaida both as "substantial," meaning an attack from either source is a strong possibility. It puts the risk of dissident IRA attacks in Northern Ireland at the higher level of "severe," meaning highly likely.
At an April 9 ceremony in a Londonderry cemetery, a masked Real IRA member told supporters the group would keep attacking police and British soldiers and "their installations, as well as British interests and infrastructure." The person didn't specify any threat to the Olympics.
An Irish anti-terrorist officer said two Oglaigh na hEireann operatives were trailed from the Irish border to London in early 2011, where they met supporters and saw several Olympics-connected sites as tourists.
The officer, who spoke to the AP on condition he not be identified because he wasn't authorized to speak to the media, said it was not clear if the dissidents were scouting Olympics sites, because their trip also preceded the April 2011 royal wedding of Prince William and Kate Middleton. The officer said the two men remain under surveillance back home.
The experts are unanimous on one key point: If any dissident IRA group does plant a bomb near the torch route or an Olympic facility, it will be to generate panic and headlines, not civilian deaths.
That means the use of telephoned warnings using recognized code words. The Provisional IRA already has demonstrated how much chaos can be caused by this tactic.
In 1997, the group used bomb threats to force 70,000 to evacuate Britain's biggest horseracing and gambling event, the Grand National. Extensive, fruitless searches for a bomb meant it took two days to relaunch the race.
But bitter experience shows that phone calls don't always work. Too often, the telephoned warnings are vague or delivered in thick rural Irish accents. Both problems meant that in Omagh, police unwittingly evacuated crowds into the bomb's path.
The homemade bombs by dissident IRA groups also are often flawed. Many are duds and some explode sooner than intended.
"The dissidents aren't in the business of planting no-warning bombs against civilian targets," said English, contrasting their behavior with that of al-Qaida militants. "But the worrying fact is, they are not as technically able as the Provisionals were. And that incompetence can make you more lethal."
Editor's note: Shawn Pogatchnik has covered Northern Ireland for The Associated Press since 1991.
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