JUBA, South Sudan — South Sudan’s president on Monday ordered a dusk-to-dawn curfew in the capital after soldiers loyal to the former deputy attempted to seize power by force, leading to clashes between military factions that highlight the growing instability of the world’s youngest nation.

Albert Lea is home to a small population of South Sudenese residents.

Flanked by government officials, President Salva Kiir —who put on fatigues with an army general’s epaulets inside of his usual gentleman’s suit — said Monday in a televised address to the nation that the military had foiled a coup orchestrated by “a group of soldiers allied with the former vice president.” The soldiers had attacked the South Sudanese military headquarters near Juba University late Sunday, sparking sporadic bursts of gunfire that continued Monday, he said.

“The attackers went and (the) armed forces are pursuing them,” Kiir said Monday. “I promise you today that justice will prevail.”

The government is now “in full control of the military situation” in Juba, he said, insisting his government could only be removed though elections.

Details of the attempted coup remained sketchy, but South Sudanese Foreign Minister Barnaba Marial Benjamin told The Associated Press Monday that troops within the main army base in Juba raided the weapons store but were repulsed. Some politicians had since been arrested, he said, but could not confirm if former Vice President Riek Machar —the alleged coup leader— was among those in detention. Benjamin said the coup was plotted by “disgruntled” soldiers and politicians led by Machar, who fell out with Kiir before being fired earlier this year as the country’s deputy president.

An Associated Press reporter saw heavily armed soldiers and police patrolling the streets of Juba, but gunfire could no longer be heard later on Monday. The streets were largely empty of civilians. EgyptAir reported that it had cancelled its flight to Juba on Monday, saying the airport there was closed.

The United Nations Mission in South Sudan on Monday reported the sound of mortar and heavy machine-gun fire, saying hundreds of civilians had sought refuge inside U.N. facilities.

“We hope the security situation in Juba will quickly normalize to enable the civilians to return very soon to their residential areas,” the mission said in a statement. There were no “key political or military figures” among those given shelter inside U.N. facilities, it said.

Tension had been mounting in South Sudan since Kiir fired Machar as his deputy in July, sparking concerns about possible tribal clashes. Machar, who has expressed a willingness to contest the presidency in 2015, said after he was fired that if the country is to be united it cannot tolerate a “one man’s rule or it cannot tolerate dictatorship.” His ouster, part of a wider dismissal of the entire Cabinet by Kiir, had followed reports of a power struggle within the ruling party. At the time, the United States and the European Union urged calm amid fears the dismissals could spark political upheaval in the country.

While Kiir is leader of the ruling Sudan People’s Liberation Movement party, many of the dismissed ministers, including Machar, were key figures in the rebel movement that fought a decades-long war against Sudan that led to South Sudan’s independence in 2011. Machar, a deputy chairman of the ruling party, is one of the country’s most influential politicians.

The local Sudan Tribune newspaper reported on its website that military clashes erupted late Sunday between members of the presidential guard in fighting that seemed to pit soldiers from Kiir’s Dinka tribe against those from the Nuer tribe of Machar.

In a message to American citizens Monday, the U.S. Embassy in Juba said it had received “reports from multiple reliable sources of ongoing security incidents and sporadic gunfire in multiple locations” across Juba.

“The U.S. Embassy has not been able to confirm that gunfire and insecurity have fully ceased,” the message said. “The embassy recommends that all U.S. citizens exercise extra caution at all times. The U.S. Embassy will continue to closely monitor the security environment in South Sudan, with particular attention to Juba city and its immediate surroundings, and will advise U.S. citizens further if the security situation changes.”

Hilde Johnson, special representative of the United Nations secretary-general for South Sudan, said in a statement that the U.N. mission in Juba was “deeply concerned” over the fighting that broke out late Sunday and which continued Monday.

“As the Special Representative of the Secretary General I urge all parties in the fighting to cease hostilities immediately and exercise restraint,” the statement sad. “I have been in touch regularly with the key leaders, including at the highest levels to call for calm.”

South Sudan has experienced bouts of ethnic violence, especially in rural Jonglei state, since the country peacefully broke away from Sudan after a brutal civil war.