Colin Kaepernick, the NFL quarterback who has used his platform to highlight racial injustice within the United States, has turned his attention to the country’s foreign policy, attacking American “imperialism” in a series of tweets on Saturday.

The former San Francisco 49ers star’s comments came after the killing of Iranian military commander Qassem Suleimani by a US drone, although Kaepernick did not mention the incident directly.

“There is nothing new about American terrorist attacks against Black and Brown people for the expansion of American imperialism,” he wrote on Twitter.

Kaepernick expanded on the topic in another tweet: “America has always sanctioned and besieged Black and Brown bodies both at home and abroad. America militarism is the weapon wielded by American imperialism, to enforce its policing and plundering of the non white world.”

America has always sanctioned and besieged Black and Brown bodies both at home and abroad. America militarism is the weapon wielded by American imperialism, to enforce its policing and plundering of the non white world. — Colin Kaepernick (@Kaepernick7) January 4, 2020

He also retweeted a quote from activist and author Angela Davis: “As a Black woman, my politics and political affiliation are bound up with and flow from participation in my people’s struggle for liberation, and with the fight of oppressed people all over the world against American imperialism.”

Republican senator Lindsey Graham was among those who pushed back against Kaepernick. “He’s a loser on and off the field,” said Graham during an appearance on Fox News. “He has no idea what the Iranian regime has done to the region. He has no idea that they have 600 American deaths as a result of IEDs made in Iran and used in Iraq.”

Kaepernick rose to fame as a quarterback for the 49ers, who he took to the Super Bowl in 2013. In 2016 he began to kneel for the national anthem, in protest at racial injustice in the US. He has been without a team since leaving the 49ers at the end of that season.

The 32-year-old has settled a claim that team owners colluded to keep him out of the league due to his political stance. A recent workout in front of NFL scouts has not led to any formal job offers.

Kaepernick’s comments came after actor Rose McGowan said Suleimani’s death had been an act of disrespect to Iran.

“Dear #Iran, The USA has disrespected your country, your flag, your people. 52% of us humbly apologize,” McGowan tweeted on Friday. “We want peace with your nation. We are being held hostage by a terrorist regime. We do not know how to escape. Please do not kill us.”

After receiving criticism for her comments, McGowan clarified her views in an interview with the Associated Press.

“I don’t support Iran over America. I want America to be better,” she said.

There is concern that Suleimani’s death could spark instability in the Middle East, and retaliation against Americans.

Donald Trump has said 52 Iranian sites that will be hit “very hard” if the country chooses to strike back against America or its allies.