A U.S. defense official says four of Iran’s Islamic Revolutionary Guard Corps ships “harassed” U.S. warship USS Nitze Tuesday in an incident that was “unsafe and unprofessional,” reports Reuters.

The altercation occurred near the Strait of Hormuz. The Iranian ships were “conducting a high-speed intercept and closing within a short distance of Nitze, despite repeated warnings,” an anonymous official told Reuters. The vessels approached within 300 yards of the USS Nitze.

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The tense exchange comes at a time of tense relations between the United States and Iran. “IRGC, the Islamic Republic’s praetorian guard, is suspicious of U.S. military activity near Iran’s borders and appears to be sticking to a familiar posture in the Gulf that predates last year’s nuclear accord between Iran and six world powers, including the United States,” reports Reuters.

Many critics of President Obama’s dangerous Iran Deal say it’s foolish to appeal to a country that supports Syrian president Bashar al-Assad and his ballistic missile program. This also comes amid reports Obama bowed to the country last year and gave them a $400 million ransom payment in exchange for four American hostages.

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The U.S. defense official told Reuters the USS Nitze attempted communication with the Iranian fleet 12 times to no response. The Nitze also set off 10 flares in the direction of the Iranian ships.

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“USS Nitze had to change course in order to distance itself from the Iranian vessels, the official said, adding that the incident could have led to a diplomatic protest, but the United States does not have diplomatic relations with Iran,” according to Reuters.

It is unclear whether the harassment was led by rogue Revolutionary Guard commanders or sanctioned by senior officials in Tehran, Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace, told Reuters.