The State Department Sunday urged U.S. citizens, including nonemergency government personnel, to leave Burundi as violence escalated in the small Central African nation. The travel warning was issued just two days after the worst violence the country had seen since a failed coup in May.

Fighting broke out Friday in the Burundian capital of Bujumbura when gunmen attacked three military bases and nearby neighborhoods. "They entered in our compounds, gathered all young and middle-aged men, took them and killed them away from their homes," a resident told Reuters.

The clashes went on throughout much of the day and resulted in 90 casualties. Police have yet to identify the gunmen, who are assumed to be rebels aiming to topple President Pierre Nkurunziza.

Unrest has been reignited in Burundi following the end of a 12-year civil war between the Hutu majority and the Tutsi minority, bubbling over in April after Nkurunziza announced he was running for a third term. The former rebel leader has governed the country for nearly 10 years since peace was brokered in 2005.

Since he was elected by Parliament for his first term, the president claims he should have the right to be elected by popular vote twice. Nkurinziza has constitutional law on his side, though many have disagreed with his right to run again. Violence erupted after he made the announcement to run again, and dozens of people have been killed in clashes since April.

Nkurunziza won the disputed presidential election in July, with 69.41 percent of the vote. Many opposition groups abstained from voting, contributing to his high margin.

More than 100,000 people have fled the country since Nkurinziza announced his intention to run for a third term, with many fearing that the unrest will trigger another civil war. More than 300,000 people were killed during the 12-year war, and the peace brokered by the president's party has been a fragile one.