The South Sudan Opposition Movements Alliance has denied involvement in the killing of civilians along the Juba-Nimule highway.
The group led by Thomas Cirilo, Paul Malong and Pagan Amum condemned the killing.
It denounces what it describes as the heinous killing of innocent civilians and members of the clergy.
SSOMA ‘statement comes after President Salva Kiir stated that the government may reconsider its position on the ongoing Sant Egidio-led Rome Initiative.
The peace process is between the government and the holdout groups, SSOMA.
President Kiir blamed the holdout group for the attack that led to the death of two reverend sisters and three other travellers on Monday.
He said the act is a violation of the cessation of hostilities agreement signed between the holdout groups and the government in Rome Italy.
SSOMA, however, accused government forces of attacking civilians.
It said the ongoing attacks on civilians along roads, ethnic fights in villages and disappearances inside the towns of South Sudan are the responsibility of the government.
The group called on the international community and relevant organizations to investigate the barbaric killings, and especially on church personnel.
SSOMA further described the recurring ambushes, attacks, and killings of innocent people along the major roads and towns in South Sudan as clear proof of the total breakdown of law.
The Saint-Egidio-led mediation is aimed at supporting an inclusive peace agreement in South Sudan by persuading the hold-out group to join the revitalized peace deal signed in September 2018.
In January last year, the government and SSOMA signed the Rome Declaration to cease hostilities.