The Iranian military has conducted a wave of cyberattacks on Obama administration officials in recent weeks, The Wall Street Journal reports.

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The attacks are believed to be connected to the arrest of an Iranian-American businessman who pushed for stronger ties between the two countries, U.S. officials told the Journal.

The attacks targeted officials in the State Department’s Office of Iranian Affairs and its Bureau of Near Eastern Affairs, as well as journalists and academics.

“U.S. officials were among many who were targeted by recent cyberattacks,” an administration official said. “U.S. officials believe some of the more recent attacks may be linked to reports of detained dual citizens and others.”

The official added that the U.S. is investigating possible links to the arrest of Siamak Namazi, who was reportedly detained by the Revolutionary Guard’s intelligence arm on October 15.

Namazi is the fourth American known to be imprisoned in Iran. The head of strategic planning at an energy company, the dual citizen was arrested while visiting family in Tehran.

Those close to Namazi say his email contacts have also become the target of cyberattacks, according to the Journal.

The arrests come at a particularly tense time in U.S.-Iran relations. While the Obama administration has expressed hope that the landmark nuclear deal reached in July could boost cooperation between Tehran and the U.S., Supreme Leader Ayatollah Ali Khamenei and other Iranian hardliners have continued to show hostility toward the U.S.

Khamenei has repeatedly accused the U.S. of using the agreement to intentionally weaken Iran’s government.

The Guard’s intelligence arm, which arrested Namazi, answers to Khamenei, not President Hassan Rouhani’s more pragmatic government. Observers say that internationally active businessmen touting a more open political and economic environment are at particular risk from hardline forces.

Compounding the tensions, Iran’s ability to conduct sophisticated cyber warfare is on the rise. Security experts now describe the country as a top-five world cyber power.

In what some critics see as a tipping point, Iran was the victim of one of the most destructive cyberattacks ever carried out, the so-called Stuxnet virus discovered in 2010.

The U.S. is believed to have worked with Israel to launch the attack during the Bush administration as a way to prevent Iran from developing a nuclear weapon. The virus disrupted about one-fifth of Iran’s nuclear centrifuges.

A recent report indicates that the country’s cybersecurity budget has skyrocketed twelvefold under Rouhani, who took office in 2013.

Officials say that Iran has built an army of hackers, reportedly trained by Russia. Moscow denies the allegation.

A late 2014 report revealed that Tehran has infiltrated the critical infrastructure networks in over a dozen countries worldwide, including in the U.S.

National security experts warn that the U.S. is dangerously vulnerable to attack on critical infrastructure.

“We have more power at our fingertips than ever before to communicate, collaborate and make transactions each day across the world we share,” Obama said in October. “Let us remind ourselves of the value of our infrastructure, while recognizing the challenges of protecting it.”