Michael Chertoff

The top U.S. security official says the recent terrorist attacks in London point to the need to monitor potential terrorist sleeper cells inside the United States.

Homeland Security Secretary Michael Chertoff told the Senate committee that oversees transportation that while it is still early to draw lessons from the recent attacks in London, it is clear that the terrorist threat is not only external.

"Although we do tend, and I think properly tend to focus on people coming in from outside (the country), we also have to focus on so-called sleeper cells inside a country and that is one of the reasons that making sure we have good intelligence, real time intelligence about what is going on with potential sleeper cells in the United States is an important component of our preventing these acts," ," Mr. Chertoff says.

Secretary Chertoff was asked about the impact of the London bombing on U.S. security efforts, especially the need to safeguard public transportation systems like subways, trains and buses.

Mr. Chertoff says there is new focus on mass transit in the wake of the attacks. But he also says the federal government must share that responsibility with state and local governments who are better positioned to add security personnel where needed.

Senators from both parties also raised concerns about port security. Democrat John Kerry of Massachusetts says the Homeland Security Department has been slow to implement a thorough inspection regime to check all cargo coming into the country.

"The country still has no plan to reroute commerce should a port be attacked and that lack of planning could prove destructive to our economy if there were a major port being closed, especially if oil or natural gas deliveries were stopped," Mr. Kerry says.

Secretary Chertoff says the department is slowly increasing the amount of cargo checked at U.S. ports. But he adds that he is committed to maintaining the free flow of commerce at the same time.

"But make sure we do not compromise the ability of our ports to operate. And that is why when people say, well, you should inspect 100 percent of the cargo, we all know that that would be the death of the port because you could not move anything through," Mr. Chertoff indicated.

Lawmakers generally praised the reorganization plan Secretary Chertoff unveiled for his department last week that he says will allow homeland security officials to react to terrorist threats more quickly.