WASHINGTON—The U.S. military is using new digital weapons to try to neutralize Islamic State’s ability to communicate, control forces and manage finances in Syria and Iraq, top Pentagon officials said Monday, providing fresh details about the newest front against the terror network.

U.S. officials have used a number of measures to counter Islamic State, also known as ISIS and ISIL. But many of these efforts have failed to prevent the group from using technology to recruit, plan attacks and move resources and money. Islamic State has used its geographic stronghold—most notably in Raqqa, Syria, and Mosul, Iraq—to train and plan attacks in the Middle East and elsewhere, and its use of technology is central to this effort.

Defense Secretary Ash Carter said the new military campaign, led by the Pentagon’s U.S. Cyber Command, is taking place particularly in Syria “to interrupt ISIL’s command and control, to cause them to lose confidence in their networks, to overload their networks so that they can’t function.”

Mr. Carter, briefing reporters on the effort alongside Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, said the attacks are aimed at doing “all off these things that will interrupt their ability to command and control forces there, control the population and the economy.”

The effort is having effects so far, Mr. Carter said, declining to provide specifics.

The new cyber-offensive comes as the Pentagon is offering more details—perhaps more than ever before—about the way Cyber Command conducts missions. Cyber Command was created in 2009, and it develops offensive and defensive weapons and capabilities.

Cyber Command is led by Adm. Mike Rogers, who is also head of the National Security Agency. He said in January that the U.S. government was at a “tipping point” when it comes to the use of cyberweapons, and he suggested the military was ready to use them in more of an offensive manner.

“Dunford and Carter are making clear that the U.S. military can and is carrying out offensive cyber-operations,” said Peter Singer, a senior fellow at the think tank New America and an expert on the development and use of cyberweapons. “Everyone knew we could do it, and this is the first public acknowledgment that we are doing it. It’s a big line to cross.”

Mr. Carter became Defense Secretary in February 2015, and he has made the development of the Pentagon’s cyber-capabilities a priority. He and Adm. Rogers are traveling to San Francisco this week to participate at the RSA Conference on digital security, a reflection of how technology is a major focus for senior military leaders.

So far, the cyberattacks against Islamic State have generated desired effects, but the U.S. is “learning more, and we’re accelerating this just as we’re accelerating everything else we’re doing in both Syria and Iraq,” Mr. Carter said.

The precise impact of the cyberattacks couldn’t be learned. For example, it was unclear whether the military had disrupted Islamic State’s use of social-media networks, such as Facebook Inc. and Twitter Inc., or if it had tried to break into the computer networks used by militants and leaders.

Mr. Carter said the hacking campaign could force Islamic State to communicate via methods more easily accessible to the U.S.

“As we disrupt the ISIL communications via cyber or other methods, sometimes we do drive them to other means,” Mr. Carter said. “Sometimes, those other means are easier for us to listen to.”

Cutting access to protected communications drives militants to “older technologies,” Mr. Carter said, making the group more vulnerable.

Mr. Carter said the U.S. has been using unspecified cyber capabilities in Mosul ahead of a campaign to retake the city. He said the U.S. effort there would be an expansion of the assistance U.S. forces provided to Iraqi troops when they retook Ramadi in December and that the U.S. is currently developing proposals for it.

Gen. Dunford said the motivating philosophy behind the cyberefforts is to isolate Islamic State in Iraq and Syria as the military campaign looks to cut off the militant group’s territory and communication networks.

“Conceptually, that’s exactly the same thing we’re trying to do in the cyberworld,” he said. “We’re trying to both physically and virtually isolate ISIL, limit their ability to conduct command and control, limit their ability to communicate with each other, limit their ability to conduct operations locally and tactically.”

The elements of surprise and confusion are critical to the campaign’s success, Gen. Dunford said.

As of last year, Cyber Command had nine “national mission teams,” with plans to build four more. Much of their operations are secret.

Dozens of countries, both large and small, have engaged in a cyber arms race in recent years, with governments developing both offensive and defensive capabilities. Many of these weapons are classified, as their public discussion can make it easy for adversaries to defend against or mimic them. For example, if one military discloses they have developed a way to attack the computer systems in a battleship, other countries could change the computer systems they use in battleships.

But the secrecy brings drawbacks. Several U.S. lawmakers have said that if the military would disclose some of its cyber-capabilities, it could serve as a deterrent from adversaries intent on attacking the U.S. Revealing cyberweapons could also serve as a signal to Congress and the public that the U.S. has a new way of countering Islamic State militants, who have so far proven more difficult than expected to contain using more traditional warfare.