Some South Sudanese, including those with dual U.S. citizenship, are not being allowed to leave war-torn South Sudan, even as the United States, India and others continued Thursday to evacuate their citizens while a fragile cease-fire appeared to hold.

The reports that South Sudan’s government is checking the political ties of people, especially of men, who are seeking safety have raised fears of further violence in a country trying to heal from civil war.

An Associated Press reporter at the airport in the capital, Juba, saw local authorities refuse about 20 dual South Sudanese-U.S. citizens from leaving the country, despite the presence of U.S. Embassy staff.

The State Department acknowledged that some people had been barred from boarding a chartered flight.

“In a July 14 security message, the U.S. Embassy advised U.S. citizens that the government of South Sudan is scrutinizing the travel documents of dual nationals, with an apparent focus on South Sudanese government and political affiliation, particularly of male dual nationals,” spokeswoman Elizabeth Trudeau said.

In a statement, Amnesty International said it had received reports from two charter airline companies that “National Security Service officers have ordered them not to carry South Sudanese nationals, particularly men.”

The London-based rights group called the restrictions “totally unacceptable” and called for safe passage for civilians.

Other South Sudanese trying to flee the country by road have reported being turned back from the border.