JUBA, South Sudan (AP) -- Disgruntled soldiers and politicians led by a former vice president attempted to overthrow the South Sudanese government, a top government official said Monday, as sporadic fighting continued between factions of the military in the latest violence to hit the world's youngest nation.

Some troops within the main army base raided the weapons store in the capital but were repulsed, South Sudanese Foreign Minister Barnaba Marial Benjamin told The Associated Press Monday. The military insisted the situation in Juba was tense but unlikely to get worse.

Some politicians had been arrested, he said, but could not confirm if former Vice President Riek Machar _who he said led the attempted coup _was among those in detention. President Salva Kiir had ordered a dawn-to-dusk curfew, he said.

Explosions and sporadic gunfire rang out early Monday in Juba amid repeated clashes between factions of the military, according to Col. Philip Aguer, the South Sudan military spokesman, who insisted later on Monday that the army was now ``in full control of Juba.''

An Associated Press reporter saw heavily armed soldiers patrolling the streets of Juba Monday amid the gunfire emerging from Juba's main army barracks. The streets were largely empty of civilians, with most Juba residents staying indoors. 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 machinegun fire, saying hundreds of civilians had sought refuge inside U.N. facilities.

Tension had been mounting in the world's youngest nation since Kiir fired Machar as his deputy in July. 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 SPLM 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.

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.