At least 13 people, including four journalists, were killed in South Sudan's western region, when gunmen attacked their convoy in the country's west, a military spokesman said.
Col. Philip Aguer Panyang blamed the attack in the western town of Raga on Tuesday on the Ugandan rebel group the Lord's Resistance Army (LRA) believed to be hiding in neighbouring countries.
Panyang told Al Jazeera that while no group had yet claimed responsibility for the attack, he was "definitely sure" that the LRA was involved, saying it was the only group with the capability to carry out such an attack in the area.
Women and children were amon the dead, he said, adding that government forces had been deployed to the region.
Earlier, Panyang told the Associated Press news agency that the rebels crossed into the country's Western Bahr el-Ghazal state from Sudan, Chad or Central African Republic.
South Sudan is struggling to contain lawlessness as conflict between the government and the rebels continues.
The fighting started in December 2013, when forces loyal to the former vice president, Riek Machar, fought the national army of President Salva Kiir's government.
The two sides have signed several peace deals brokered by neighbouring governments, but none has actually stopped the warfare in the oil-rich country.
Since the violence began, more than 1.7 million people have fled their homes and thousands have been killed.
Humanitarian officials have warned that South Sudan risks falling into a famine situation this year if the violence does not end and people do not return home to plant crops.