Former CIA Director John Brennan John Owen BrennanJournalism or partisanship? The media's mistakes of 2016 continue in 2020 Comey on Clinton tweet: 'I regret only being involved in the 2016 election' Ex-CIA Director Brennan questioned for 8 hours in Durham review of Russia probe MORE on Tuesday blasted the Trump administration for its stance on Iran, saying that President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's hard-line posture toward Tehran and disavowal of a landmark nuclear deal had ultimately diminished the possibility of peaceful political change there.

"With wholesale condemnation of Iran and nuclear deal over past year, Trump Admin squandered opportunity to bolster reformists in Tehran and prospects for peaceful political reform in Iran," Brennan tweeted. "Bluster is neither a strategy nor a mechanism for exercise of U.S. power and influence."

With wholesale condemnation of Iran and nuclear deal over past year, Trump Admin squandered opportunity to bolster reformists in Tehran and prospects for peaceful political reform in Iran. Bluster is neither a strategy nor a mechanism for exercise of U.S. power and influence. — John O. Brennan (@JohnBrennan) January 2, 2018

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Brennan, who served as CIA director during the Obama administration, has been a frequent critic of Trump's foreign policy and has also fired back at the president's disparaging comments about the U.S. intelligence community.

Widespread demonstrations across Iran have raged since last Thursday, leaving at least 21 people dead. So far, 450 people have been arrested in the protests.

The protests have largely expressed ire toward Iran's leaders for failing to deliver on the economic growth that they had promised as a result of a 2015 deal with the U.S. and other countries to curb Tehran's nuclear ambitions.

Protesters have also voiced anger at what they see as the government's willingness to widen involvement in the region, while putting domestic issues on the back burner.

The demonstrations are the largest in Iran since 2009 after the election of former Iranian President Mahmoud Ahmadinejad.

Iran's economy has long suffered under international sanctions. But the country's leaders promised an economic boom under the 2015 nuclear deal, which provided some sanctions relief.

Trump disavowed that deal in October, though the U.S. has not reimposed sanctions lifted under the framework.