WASHINGTON (CNN) -- "Current evidence" does not show the people involved in an alleged plot to blow up airplanes planned to conduct any operations in the United States, Department of Homeland Security Secretary Michael Chertoff said Sunday.
"The current evidence does not show any plotting occurring inside the United States or any plan to conduct operations within the United States," Chertoff told CNN's "Late Edition."
Chertoff's remarks came three days after police in England arrested about two dozen people allegedly involved in a plot to use liquid explosives to blow up as many as 10 passenger planes during flights from the United Kingdom to the United States.
That prompted an immediate ban on liquids and gels in carry-on luggage in the UK and U.S. that resulted in widespread flight cancellations and delays. (Watch why checking in bags may not keep planes safe -- 1:58)
On Sunday, the Transportation Security Administration exempted small doses of liquid medications, glucose gel for diabetics, solid lipstick and baby food from the list of items passengers are not allowed to take onto planes. All aerosols are prohibited.
The TSA also said it will require all passengers to remove their shoes for X-ray screening.
"These tweaks are aimed at making a smoother process at the checkpoint," TSA Assistant Secretary Kip Hawley said in a news release.
Asked about suggestions that some of the alleged plotters had telephoned people in the United States, Chertoff said, "As of now -- and of course it's subject to change -- we do not see any plotting inside the United States or any indication of operational activity by these plotters inside the United States."
Chertoff described the alleged plot as "sophisticated," but said officials have not determined whether it was the work of the al Qaeda terrorist organization responsible for the September 11 terrorist attacks.
Chertoff described as "not accurate" an Associated Press story that said "the Bush administration quietly tried to take away $6 million that was supposed to be spent this year developing new explosives detection technology."
"Lawmakers and recently retired Homeland Security officials say they are concerned the department's research and development effort is bogged down by bureaucracy, lack of strategic planning and failure to use money wisely," the report stated.
"The department failed to spend $200 million in research and development money from past years, forcing lawmakers to rescind the money this summer."
Chertoff said that, in fiscal year 2006, the federal government has spent nearly $800 million on detection research and deployment.
"There had been some discussion before this plot was discovered about moving a very small amount of that money to plug a budget shortfall in the security measures around federal buildings, but we rejected that before this plot was actually discovered," he said.
"We have tried not to simply shovel it out the door at every new technology or every new idea. And so we have not spent all the money," he said. "But it doesn't mean that the money has lapsed or that it won't be spent. ... We want to be strategic."
Chertoff also rejected an editorial in Saturday's New York Times that said the government and airline executives "have been aware of the liquid bomb threat for years, but have done little to prepare for it."
The editorial "reflects ... a lack of understanding of what we are doing," he said.
He said the department trained 38,000 screeners "in modern techniques for spotting detonators," and had run pilot projects "particularly focused on liquid explosives."
But the issue is complex, he added. Because explosives can be fashioned from common chemicals, detectors must not cast too wide a net of suspicion if they are to be useful.
"We don't want a system that has so many false positives that we have hours and hours waiting on line at the airport because we have to open every bottle and every cosmetics case," he said.
Asked why security officials had not previously stopped travelers from carrying liquids onto planes, he said details uncovered during the recent investigation led to the change.
"It was the sophisticated nature of the disguised bombs, I think, that caused us to take the step of making sure that we could protect American travelers by stopping liquids from coming on the plane, at least for a period of time," he said.
Asked whether screeners would have stopped the alleged plotters from carrying the liquids aboard planes, he told "Fox News Sunday," "It's actually unclear whether we would have or not.
"But of course, until we can ascertain that our techniques allow us to spot this kind of plot, we want to make sure we're safe rather than sorry."
And American fliers are now indeed safe, he told CBS' "Face the Nation."
"It is safe to fly. And it's safe to fly particularly because of the measures we have put into place."
Democrat: DHS 'stretched thin'
Rep. Ed Markey, a Massachusetts Democrat and a senior member of the House Homeland Security Committee, was not impressed.
In a written statement, he accused the Bush administration and the Republican-led Congress of continuing "to nickel-and-dime homeland security, while writing a blank check for the war in Iraq."
"This has left our homeland security defenses stretched thin, with not enough screeners and technology to cover the known threats," he said.
"As a result, the Bush administration seems to lurch from crisis to crisis, covering yesterday's vulnerabilities but leaving tomorrow's threats wide open to exploitation by terrorists."
Markey cited the 1994 bombing with liquid explosives of a Philippines airliner, and blamed the Department of Homeland Security and the TSA for failing to heed the warning.
More than a decade later, "Chertoff can only point to a handful of pilot programs to detect such explosives. And while he says that many TSA screeners have been retrained to catch such terrorist scenarios, he doesn't seem to know if a liquid bomb plot could be foiled by TSA or DHS."
Markey said terrorists could exploit continuing vulnerabilities, including a failure of authorities to inspect checked baggage and the fact that the names of passengers on international flights are sometimes not checked against "no-fly" lists until after planes have taken off.