The United Nations Security Council said Wednesday that the attack on the UN's base in Bentiu town of South Sudan's Unity state last week may constitute a war crime.

Last week the United Nations Mission in South Sudan noted that on Monday 25 April a rocket propelled grenade was "directly targeted" at its base in Bentiu where more than 100,000 civilians have taken shelter.

According to a press release, the Security Council "condemned in the strongest terms the attack against the UNMISS compound in Bentiu on 25 April, while stressing that attacks directed against civilians, UNMISS personnel and United Nations premises are unacceptable and may constitute war crimes."

Last week, UNMISS said: "Initial investigations indicate that the projectile, along with earlier small arms fire, was directly targeted at the UNMISS compound. The location of the UNMISS compound is well known and there were no known armed forces in the vicinity of the base at the time of the attack."

However, UNMISS chief Ellen Loej instead told reporters today in Juba that while the incident was "extremely regretable" she did not know if the base was directly targeted or not.

"We are trying to investigate to find out what really happened behind because before we start pointing fingers we have to find out whether it was an accident or whether it was deliberate," Loej said.

Loej said there are quite a number of armed groups in and around Bentiu and they are trying to find out what the intention really was of the people who fired the grenade into the base.

"It could have been they had fired at somebody on the other side of the camp and it fell down," she said. "If it was directly aimed at a UN camp it's extremely serious, because then it's a direct attack on the UN, so that's why we have to be very clear on what it was, to talk to the parties before we jump to conclusions."

The attack occurred amid clashes involving cattle rustlers which left one person dead, which Radio Tamazuj reported on earlier.

Bentiu has been in control of South Sudan's government forces for more than a year.