Former Pentagon chief Jim Mattis issued a stinging rebuke of his previous boss President Donald Trump on Wednesday and accused him of trying to “divide” America and failing to provide “mature leadership” as the country reels from days of protests.

Mattis had resigned in December 2018 over Trump’s ordering of a full troop withdrawal from Syria, also voiced support for the demonstrators whose anti-racism rallies have roiled the country.

Mattis wrote in a statement posted online by The Atlantic, “Donald Trump is the first president in my lifetime who does not try to unite the American people — does not even pretend to try”.

“Instead, he tries to divide us,” continues the retired Marine general, who had previously argued it would be inappropriate for him to criticize a sitting president.

“We are witnessing the consequences of three years without mature leadership,” he stated.

Mattis also expressed his anguish after witnessing events of the last week, which saw Trump threaten a military crackdown as nationwide protests turned violent in some cities.

Minnesota took one of the first concrete actions to address the grievances behind the uprising, which began after Floyd’s death on May 25 in the state’s largest city Minneapolis.

George Floyd, a 46-year-old African-American, was handcuffed and pinned to the ground in Minneapolis on May 25 by a white police officer who kneeled on his neck as he gasped for breath.

The protests turned violent across the US that left at least five people dead and over 4,000 people arrested.

Mattis wrote that the protesters’ call for equal justice was a “wholesome and unifying demand — one that all of us should be able to get behind.”

The photo op has become a lightning rod for criticism of Trump’s handling of the crisis, with religious leaders, politicians, and onlookers around the country expressing outrage.

“When I joined the military, some 50 years ago, I swore an oath to support and defend the Constitution,” Mattis states.

Police and protesters clashed in numerous cities including Chicago and New York, with officers responding to projectiles with pepper spray while shop windows were smashed in Philadelphia.

Most of the shops in downtown Manhattan have had plywood installed over their windows and entrances, and workers were boarding up more shops on Tuesday afternoon, bracing for another potentially violent night.

The United States also faced unusual, if polite, criticism from some international allies including Germany, Britain and Australia.

German Foreign Minister Heiko Maas called the anti-racism protests “understandable and more than legitimate.”

(With inputs from agency)