The FBI warned law enforcement and high-tech companies to be on guard for possible terrorist activity that could use or affect the Internet, government officials said Wednesday.

The alert warned of possible attacks on or through utility, municipal and state information systems, said Gordon Johndroe, spokesman for the White House office of homeland security.

It was not specific in its time frame or geographic area, he said.

The warning went to 18,000 law enforcement agencies and some technology firms, an FBI official said.

The official said the alert, issued by the FBI's infrastructure-protection arm, was less urgent than the general alerts the Bush administration has issued to all Americans.

The government has called on law enforcement personnel across the nation to remain vigilant against domestic terrorism until March 11, extending a standing alert through the Winter Olympics in Salt Lake City.