Ongoing violence in the world's youngest country, South Sudan, is being perpetrated by government troops, a new report by Amnesty International revealed.

The report, released on 21 May, shows that there has been a surge in government activity that includes the killing, abduction and sexual assault of civilians by military troops.

Michelle Kagari, deputy director at the aid organisation, said: "The spike in fighting between the parties to the conflict is a clear indication that South Sudan's leaders have little interest in a cessation of hostilities, while the region and the rest of the international community are reluctant to take bold steps towards addressing repeated atrocities."

According to the report, thousands of South Sudanese are fleeing to the United Nations base in Bentiu after fighting in Unity state has intensified between government forces and the Sudan Peoples' Liberation Movement/Army-In Opposition.

The newly created country plunged into conflict nearly 18 months ago as pro-government forces battled with rebels supporting President Salva Kiir's former deputy, Riek Machar.

Witnesses told Amnesty International that government forces have set villages on fire, stolen livestock and property, beaten and killed villagers and committed acts of sexual violence on women and children.

One woman said that she witnessed as her 23-year-old cousin was raped by government troops. "I saw her when I was running. She was screaming," the witness said. She told Amnesty International that her 13-year-old sister and 15-year-old brother had also been abducted.

Reuters reported that the United Nations's children's fund has said that children as young as seven have been raped by troops.

The US Department of State condemned the violence with a strongly worded statement released on 20 May.

"Violations of international humanitarian norms, including the outright targeting of civilians already vulnerable to greater harm, especially women and children, and grave human rights abuses and violations of international humanitarian law by all sides are unacceptable," the statement by Deputy Department Spokesperson Marie Harf said.

"The international community will hold those who perpetrate such abuses and violations to account."

According to The Associated Press, various aid organisations have had to pull out of battle zones, leaving thousands of civilians in need of protection.

"You have a level of violence which is unheard of," Yves Daccord, director general of the International Committee of the Red Cross told Reuters. "There is no respect...It's all about revenge, nothing else."

The government appears to be attempting to secure oil fields it desperately needs to keep running, the AP noted. On 20 May, rebel forces said they were set to take the oil fields of Paloch in Upper Nile state, however the government said troops had stopped the attack. The continued fighting over the oil fields have sent civilians fleeing for their lives.

While the South Sudan government denies all charges, the United Nations said intense fighting had been resumed near the town of Melt in Upper Nile state. Four civilians were killed on 19 May when two mortar bombs exploded inside a UN compound, the AP reported.

"It remains unclear who is in control of the town," deputy spokesman for the UN secretary-general Farhan Haq said.

The AP reported that journalist Pow James Raeth was shot and killed on 20 May by unknown assailants in Akobo, Jonglei state. Raeth is the sixth journalist to be killed in South Sudan in 2015.