LONDON — The United States has opened a new line of combat against the Islamic State, directing the military’s six-year-old Cyber Command for the first time to mount computer-network attacks that are now being used alongside more traditional weapons.

The effort reflects President Obama’s desire to bring many of the secret American cyberweapons that have been aimed elsewhere, notably at Iran, into the fight against the Islamic State — which has proved effective in using modern communications and encryption to recruit and carry out operations.

The National Security Agency, which specializes in electronic surveillance, has for years listened intensely to the militants of the Islamic State, and those reports are often part of the president’s daily intelligence briefing. But the N.S.A.’s military counterpart, Cyber Command, was focused largely on Russia, China, Iran and North Korea — where cyberattacks on the United States most frequently originate — and had run virtually no operations against what has become the most dangerous terrorist organization in the world.

A review of what should be done to confront the Islamic State is on Mr. Obama’s agenda on Monday, when he is scheduled to attend a conference in Hanover, Germany, with the leaders of Britain, France, Italy and Germany. Of these efforts, the cybercampaign is the newest. It is also the one discussed in least detail by officials of many countries, and its successes or failures are the most difficult to assess from the outside.