(Reuters) - The FBI is getting more aggressive in pursuing cyber criminals and expects to announce searches, indictments and multiple arrests over the next several weeks, the agency's official in charge of combating cyber crime said on Wednesday.

"There is a philosophy change. If you are going to attack Americans, we are going to hold you accountable," the FBI's Robert Anderson told the Reuters Cybersecurity Summit in Washington. "If we can reach out and touch you, we are going to reach out and touch you."

Anderson said the FBI would show "a much more offensive side" to its cyber program, which he took over in March.

He cited the previously unreported indictment of Dimitry Belorrossov as an example of a recent success in the agency's battle against cyber crime.

The Russian national was arrested at an airport in Spain last year and lost an extradition battle after being accused of running a botnet that attacked some 7,000 Americans, a case that Anderson said was relatively small compared to some that are in the FBI's pipeline.

Still, the arrest was one of a few that prompted Russia to warn its citizens to be careful traveling to countries having extradition treaties with the United States.

Anderson said the FBI would not be deterred from pressing charges against suspected cyber criminals who lived in countries that refused to cooperate in extraditing them.

In the past, the agency has avoided naming overseas suspects in cases where they could not be extradited in a bid to avoid embarrassing other nations.

"There's a lot of countries that will not extradite. That will not stop us from pressing forward and charging those individuals and making it public," he said.

Anderson said more criminal hackers are going to be arrested under his watch, rather than turned into sources of knowledge about how the underground operates.

But there can be exceptions when it comes to national security priorities, he added.

Most notably, the leader of the LulzSec hacking group, Hector Monsegur, has had his sentencing delayed more than a half-dozen times as he cooperates and helps break into high-value intelligence targets overseas, according to court records.

Anderson declined to say how many such hackers are helping the government in that way.

Jim Lewis, a senior fellow with the Center for Strategic and International Studies with strong ties to the intelligence community, estimated that the FBI might work with about a dozen such hackers, more than in previous years.

Anderson declined to comment on the status of the probe into a weeks-long cyber attack on retailer Target Corp (TGT.N) that came to light in December. The investigation is being led by the Secret Service.