Secretary of State Marco Rubio said Saturday that the United States was revoking all visas held by South Sudanese passport holders, accusing the African nation's government of “taking advantage of the United States.”

“Every country must accept the return of its citizens in a timely manner when another country, including the United States, seeks to remove them,” Rubio said in a statement, adding that “South Sudan’s transitional government has failed to fully respect this principle."

Besides revoking visas, Rubio said the U.S. would "prevent further issuance to prevent entry into the United States by South Sudanese passport holders.”

South Sudan’s political landscape is fragile and recent violence between government troops and armed opposition groups has escalated tensions.

Last week, United Nations Secretary-General Antonio Guterres urged regional and international leaders to prevent South Sudan from falling “over the abyss” into another civil war.

Guterres warned that the world’s newest and one of its poorest countries is facing “a security emergency” with intensifying clashes and a “political upheaval” culminating with last week’s arrest by the government of First Vice President Riek Machar.