Washington ? The deadly Spanish commuter-train bombings prompted the Homeland Security Department on Friday to advise state and local officials to boost security measures on rail transportation nationwide.

Asa Hutchinson, the agency’s undersecretary for border and transportation security, spoke with state homeland-security advisers and officials of major transit systems also to share what the Homeland Security Department knew about the Madrid bombings.

Despite heightened anxieties caused by the carnage, Hutchinson said his agency had no immediate plans to raise the nation’s terror-alert level, which is at yellow, or elevated.

He said the department had encouraged a more visible law enforcement presence at train stations and along transit lines.

In addition, he said the agency recommended deployment of additional explosive detection teams and greater use of public announcements to get the millions of Americans who use rail and mass transit to watch for suspicious activity.

Some transit systems were adding undercover riders in an effort to thwart similar bombings in the United States.

“We have no specific indications that terrorist groups are considering such attacks in the near term,” Hutchinson said. But “in the last couple of years we have had general information that indicated that mass transit is a target of al-Qaida.”

Hutchinson warned that it was uncertain what the bombings might portend for the United States because it was still unclear what group was responsible.

U.S. officials worry that if al-Qaida or an affiliated group is responsible, it could foreshadow similar bombings in the United States.

Members of the New York City Police Department's Hercules unit patrol New York's Grand Central Terminal during the morning commute. Homeland Security officials were taking extra precautions after Thursday's terror bombings in Spain.

“One of things that give you cause for concern is the level of complexity in the attacks and the coordination and the simultaneous nature of it, which all is a characteristic of the capability and style of al-Qaida,” Hutchinson said. “That’s not to say it’s them, but that certainly gives you some concern.”

Compared with how tight aviation security has become since Sept. 11, security on rail and mass transit systems appears to be little changed since before the 2001 attacks.

The 100 percent passenger and bag screening required in commercial aviation is “not a solution” for what has been a “very open rail transportation system,” Hutchinson said.

He added that there were increased security measures passengers didn’t necessarily see, such as surveillance cameras and biological sensors that sniff the air for biowarfare agents such as anthrax.

Still, the safeguards are inadequate, said Hank Chase, a homeland security expert in the Washington, D.C., area.

“We’ve done hardly anything with regard to rail traffic,” Chase said. “Passengers aren’t screened, bags aren’t screened, we’re hugely vulnerable.”

Meanwhile, the challenge of securing the thousands of miles of railbeds, tunnels, bridges and stations would carry a “humongous price” the nation could barely afford, he said.

Sophisticated explosive device sniffers at train stations would be a big improvement, but the technology isn’t up to the task yet, Chase said.

The Madrid bombings “scared the dickens out of me,” he said. “If this is al-Qaida … it bodes very ill for this country.”