Washington

US CYBER COMMAND on Thursday conducted online attacks against an Iranian intelligence group that US officials believe helped plan the attacks against oil tankers in recent weeks, according to people briefed on the operation.

The intrusion occurred the same day US President Donald Trump called off a strike on Iranian targets such as radar and missile batteries.

But the cyberoperation was allowed to go forward because it was intended to be below the threshold of armed conflict - using the same shadow tactics that Iran has used.

The online attacks, which had been planned for several weeks, were ultimately meant to be a direct response to both the tanker attacks this month and the downing of a US drone last week, according to the people briefed on the operations.

Multiple computer systems were targeted, according to people briefed on the operations, including those believed to have been used by an Iranian intelligence group that helped plan the tanker attacks.

An additional breach, according to one person briefed on the operations, targeted other computer systems that control Iranian missile launches.

Determining the effectiveness of a cyberattack on the missile launch system is particularly difficult. Its effectiveness could be judged only if Iran tried to fire a missile and the launch failed.

The online operation was first reported on Friday by Yahoo News. Few details are known, but the breach was meant to take the Iranian intelligence group offline for a time, similar to one that temporarily took down Russia's Internet Research Agency in November during and immediately after the US mid-term elections.

Beyond the cyberoperation, military and intelligence officials also are trying to devise other operations that would not escalate tensions with Iran but would try to deter further attacks, according to current and former officials.

On Saturday, Christopher Krebs, director of the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency, issued a warning about Iranian cyberattacks on American industries and government agencies, saying "malicious cyberactivity" was on the rise. NYTIMES