The string of canceled or delayed international flights over the holidays shows that security officials are loath to take risks when it comes to the flying public, aviation and intelligence experts said.

"We are operating in a high-threat environment right now and so there is very, very little margin for error," said terrorism analyst Brian Jenkins. "If people are going to make mistakes, whether they're mistakes or not, they're going to err on the side of safety rather than take unnecessary risks."

Ed Block, president of the National Association to Prevent Air Crashes (search), said officials will be double-checking terror watch lists to nail down information to "weed out anybody that's a potential" terrorist.

But some say there are still security loopholes that need to be addressed, including the lack of a comprehensive terror watch list.

At least seven U.S.-bound planes were grounded within the past week.

Not only were some British Airways (search) flights from London's Heathrow Airport to Washington canceled based on intelligence, but there have also been security issues with recent Air France flights, and one U.S.-bound flight from Mexico. Several people were questioned and some passengers were re-screened.

"I think it's pretty clear that the intelligence has gotten pretty specific," said Steve Pomerantz, a former FBI counterterrorism chief. "No longer is this just an elevation and so-called background chatter ... so they're able to take more specific action."

Some U.S. officials said there is specific, yet unsubstantiated threat information about some of these flights.

"We just don't know enough information to dismiss it, so when you have actionable intelligence — even if unsubstantiated — you move on it," one U.S. official told Fox News. "We are taking whatever precautions necessary."

Erring on the Side of Caution

Some of the delays and groundings are coming under fire.

French officials reportedly are debating the accuracy of FBI intelligence that led to the grounding of three Air France (search) flights during Christmas week. Information suggested that one person who was to have flown was a Tunisian with terror links.

A name similar to the Tunisian's appeared on one of the flight manifests, but turned out to be a 5-year-old child, FBI officials said.

"This was not a mistake … this is the process," a law enforcement source told Fox News.

"Frankly, I'm very pleased we are erring on the side of caution in these incidents," added Sen. Kay Bailey Hutchison (search), R-Texas, who sits on the Senate Commerce, Science and Transportation Committee and the panel's aviation subcommittee. "It's much better to cancel a flight than to make a mistake. I think we want to do better but we're doing a lot more than we've done before."

But some experts say despite U.S. attempts to be better safe than sorry, intelligence should be good enough to produce results.

"If we continue to make mistakes, it's like the fellow who cried wolf. After a while, we won't be taken seriously and that's when someone will slip through," former Secretary of State Lawrence Eagleburger (search) told Fox News.

One thing that needs to be created, analysts said, is a master terror watch list. The Terrorist Screening Center announced by the U.S. government on Sept. 16 aims to consolidate various lists of potential terrorists and provide round-the-clock operational support for federal screeners across the country and around the world.

Currently, many U.S. agencies have their own lists and don't share information as effectively as they should. The Bush administration has identified this as a problem and is charging the Department of Homeland Security to remedy the situation.

A lack of a comprehensive list is "a serious problem that needs to be corrected, if it can, and will be less likely to make these mistakes, if they are indeed mistakes," Eagleburger said.

But various reports say that the system is not yet 100 percent effective and that some agencies still are not submitting their own individual lists for compilation.

"Sadly, we're having to confront safety and security versus commerce and convenience," Block said.

Among other things, he added, "you have these personal liberty issues ... that are going to conflict with us nailing down this one overall watch list and that's going to continue to be a problem … but we're certainly on our way of bringing together all these varying interests together."

'A Heck of a Lot Better Than it Was Before 9/11'

Experts said more needs to be done before potential terrorists even make it to the airports to avoid such groundings and delays.

"Once you're at the airport, that's your third line of defense," Marvin Badler, the former security chief of Israel's El Al Airlines (search), told Fox News.

But others said it's not always that easy.

"The problem is, being able to respond in time to these things" prior to departure, said Billie Vincent, a former Federal Aviation Administration security chief. "The possibility of last-minute changes and so on renders it virtually impossible to prevent things like this from happening.

"We have to find a way to rationalize this process and do it better prior to departure," Vincent continued. "I'm not sure there's any easy solution to this but we have to find it."

Former FBI agent Bob Pence noted that many Asian, Middle Eastern and other names can be confusing, with many people from those countries having the same name. Plus, through the reservation process, the names can get mixed up, and that could cause some screening confusion.

"We still have to perfect that and sometimes the names are conveyed wrong," Pence said. "It isn't a perfect system yet but it's a heck of a lot better than it was before 9/11."

Fox News' Mike Emanuel, Molly Henneberg and Anna Stolley contributed to this report.