The African Union slammed the United States for banning refugees after centuries of taking black people from Africa to work as slaves. The head of the 53-member body called Trump’s ban on immigration from seven Muslim-majority countries “one of the greatest challenges” for the continent.

Nkosazana Dlamini-Zuma's remarks came during an African Union two-day summit in Addis Ababa. Zuma, a South African lawmaker and the first female leader of the African Union, said the new Trump administration could usher in “very turbulent times.” 

“The very country to which many of our people were taken as slaves during the transatlantic slave trade has now decided to ban refugees from some of our countries,” she said during the gathering in Ethiopia. “What do we do about this? Indeed, this is one of the greatest challenges to our unity and solidarity.”

For more than 300 years, Africa supplied the capital for a slave trade that sent 12.5 million people to the New World between 1525 and 1866. Only 10.7 million people survived the trip and ended up in North America, the Caribbean and South America.

Trump announced the 120-day immigration ban Friday, and defended the move throughout the weekend through his Twitter account, denying that the ban specifically prohibited Muslims from traveling to the U.S. The ban affects three African nations – Libya, Somalia and Sudan – and four Middle Eastern countries – Syria, Iraq, Yemen and Iran.

Meanwhile, the United Nations Secretary General urged African leaders Monday to embrace refugees and people fleeing violence. "African nations are among the world's largest and most generous hosts of refugees," Antonio Guterres said during the African Union meeting. "African borders remain open for those in need of protection when so many borders are being closed, even in the most developed countries in the world."

The African Union also voted this week to allow Morocco, the only country on the continent that is not a member of the alliance, to rejoin the bloc after a dispute over rebel groups.

"Morocco is now a full member of the African Union. There was a very long debate but 39 of our 54 states approved the return of Morocco, even if the Western Sahara question remains," Senegalese President Macky Sall told journalists.