ADDIS ABABA (Reuters) - The head of the African Union said on Monday that a U.S. travel ban on seven Muslim-majority countries including three in Africa heralded “turbulent times” for the continent. Nkosazana Dlamini-Zuma spoke after U.S. President Donald Trump’s executive order halted travel by people with passports from Libya, Somalia, Sudan and four other Middle East nations for 90 days, and stopped refugee resettlement for 120 days. “We are entering very turbulent times,” Dlamini-Zuma told African leaders at the start of a summit in the 54-nation bloc’s headquarters in the Ethiopian capital. “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. What do we do about this? Indeed, this is one of the greatest challenges to our unity and solidarity,” the AU Commission chief added. Even before the travel ban was announced last week, African capitals had watched the transition from Barack Obama’s administration to Trump with some concern, fearing his focus on “America first” could push trade and other ties with the continent down the U.S. list of priorities. The new U.N. secretary-general, Antonio Guterres, also hinted at unease about the U.S. administration’s actions in his address at the summit, without mentioning Trump or the United States. “African nations are among the world’s largest and most generous hosts of refugees. African borders remain open for those who need protection, when so many borders are being closed even in some of the most developed countries in the world,” said Guterres, who took over at the U.N. helm this month. 