Human rights organisations have called on President Salva Kirr to veto the National Security Service Bill, fearing it could turn South Sudan into an oppressive police state.

Human Rights Watch have warned that the bill would "allow the security service virtually unfettered authority to arrest and detain suspects, monitor communications, conduct searches, and seize property".

Since it gained independence in 2011, South Sudan has been marred with internal civil war and border disputes with Sudan.

It has been heavily criticised by human rights organisations for its security services' use of intimidation and unlawful detainment of journalists, as well as its use of heavy media censorship, particularly since the internal conflict started in December 2013.

The controversial bill, which passed through the National Legislative Assembly for a third time a week ago, would give South Sudan's National Security Service (NSS) sweeping powers.

The bill would mark a stark change from the NSS's limited intelligence power and would effectively grant them the authority to hold detainees outside the parameters of international human law.

With their potential new powers, South Sudan could become a police state as the bill contains no safeguards to restrict the NSS's authority under international law.

Human Rights Watch have also condemned the vagueness of the bill, warning that it allows the security services to illegally hold detainees in unofficial locations and could prevent them from having access to lawyers.

In their report, Human Rights Watch also said: "There are also no explicit safeguards against inhuman or degrading treatment or punishment, or torture."

"Nor does the bill stipulate that detainees will have basic due process rights, including the right to inform a lawyer or relative of their arrest, the right to counsel, or the right to be tried within a reasonable period of time."

The bill also fails to specify when security service officers need to ask a judge to issue a legitimate arrest or search warrant. Instead, civilians have no protected rights against an unsolicited security search of their property or detainment.

The latest version of the bill has been viewed as a slight improvement from one of its earlier version which had previously provided security agents with "broad criminal immunity".

President Kiir has been urged by international human rights organisations to send the bill back to parliament to be revised.