The White House appears to be taking a different approach to the second round of bombings in London in just two weeks — quietly monitoring events, with President Bush making only limited comment during a morning speech to the Organization of American States.
"They don't understand that when it comes to the defense of universal freedoms, this country won't be frightened," the president said Thursday during an appearance before members of the OAS.
Without specifically referring to the London attackers, Bush said terrorists, described as "cold-blooded killers who embrace an ideology of hatred," want to scare the rest of the world.
"They understand when they kill in cold blood it ends up on our TV screens and they're trying to shake our will. And they're trying to create vacuums in which their ideology can move," Bush said.
At the White House, press secretary Scott McClellan said that U.S. mass transit systems remain on high alert since the bombings in London two weeks ago.
"We're monitoring the situation closely," he said of the situation in London.
Aides said Bush was briefed by White House chief of staff Andy Card and National Security Adviser Stephen Hadley on Thursday's incidents. The briefing came at the end of the president's daily intelligence briefing. The president received a second briefing after his speech.
White House officials said the U.S. intelligence community is evaluating what the attacks in London could mean for the United States, and considerable manpower is being spent to assist in the investigation.
Officials said they are concerned about copycat attacks of lesser severity and effectiveness by the same group responsible for the July 7 bombings.
Three London Underground stations were evacuated at midday Thursday, and the London police commissioner confirmed that four explosions occurred in the subway and on a bus. The Fire Brigade was investigating a report of smoke at one station.
Emergency services personnel also responded to an incident on a bus in the Hackney neighborhood. The driver reported that the windows on the top deck of the double-decker bus were blown out, but no injuries were reported by Scotland Yard.
U.S. officials said that the reaction in London, with first responders wearing chemical suits, was not an indication that they suspected a biological weapons attack but that they were taking all necessary precautions.
London police said one injury was reported in one of the subway incidents. Two weeks ago, 56 people died in four homicide bombings at three London Underground stations and on a London bus.
One man arrested in Pakistan in relation to the bombings on July 7 is Haroon Aswat. A law enforcement source told FOX News that Aswat is an alleged Al Qaeda operative who is referenced in two U.S. terrorism cases as an unindicted co-conspirator.
One case involves James Ujaama, an American accused of attempting to set up a jihad training camp in Bly, Ore. The source confirmed to FOX News that law enforcement officials believe Aswat was in Seattle in 2000, likely visiting the proposed camp site in Oregon, and may have been in the United States since then.
The source said it is believed that Aswat trained in Al Qaeda camps in Afghanistan. U.S. officials are in close contact with British authorities over Aswat, who is connected to radical London cleric Abu Hamza.
Asked if the United States is done investigating Aswat, the source said, "Whenever we have an investigation of this scale, involving one of our principal allies in the War on Terror, we are far from done."
When Ujaama pleaded guilty, it was only to aiding the Taliban and not to setting up a training camp.
Back in Washington, D.C., Metro officials said the city's subways will see an increase in security and bomb-sniffing dogs in response to events in London. Buses could also face random searches.
On Capitol Hill, U.S. Capitol Police released a statement that it is "aware of no credible threats to the Capitol complex" and is keeping its "security enhancements" on high alert on Capitol grounds.
The House chaplain opened the day's proceedings with a prayer for any victims. Rep. Bob Menendez, D-N.J., said the two days of attacks in London and 2004 bombings in Madrid should send a signal to the United States to fund further mass transit security.
"Instead of acting as a wakeup call, Congress seems to be hitting the snooze button," Menendez said. "How many warnings do we need before we take action?"
Congress is debating whether to spend $100 million or more to secure trains, buses and subways across the nation. Department of Homeland Security Secretary Michael Chertoff has been reported to say that it's up to state and local authorities to provide the majority of security for their local mass transit systems.
Several lawmakers criticized Chertoff's comments, suggesting that he was abdicating federal responsibility for the security of the nation. Rep. Bennie G. Thompson, a Mississippi Democrat and ranking member on the Homeland Security Committee, said, "We know there is no endless pot of money, but it is only reasonable that our nation spends more than six-tenths of a penny for each of our 30 million daily commuters, which is all it spends now."
Chertoff, who was keeping plans to travel to St. Paul, Minn., on Thursday to meet with local officials on Friday, was monitoring the London situation, his spokeswoman Kathleen Montgomery said. She added that DHS has no plans to change the overall terror threat level at this time, which is mid-level, or yellow, except in U.S. transit, where it is at the second-highest threat level.
Homeland Security Assistant Secretary Brian Besanceney said that as a result of Thursday's second round of explosions in London, it's unlikely that orange-level transit designation will go down any time soon.
"We're going to have to take a look at the material that came out of the U.K.," Besanceney said. "And that will factor into the discussions."
Pentagon security was upgraded in response to the latest news from London, though spokesman Bryan Whitman said the building, which is adjacent to a Washington-area subway stop, had heard of no specific threats.
At the State Department, deputy spokesman Adam Ereli said no early reports have come in on American citizen injuries. He invited Americans concerned about friends or family members in London to call a State Department toll free number: 1-888-407-4747.
Ereli said the U.S. Embassy in London was temporarily closed to the public except for emergencies.
FOX News' Wendell Goler, Catherine Herridge, Amy Kellogg and The Associated Press contributed to this report.