Young men shot dead 15 people in South Sudan's eastern Pibor region, including a county commissioner, a senior official said on Wednesday, amid a rise in local conflict ahead of a national election due at the end of the year.

A civil war that erupted two years after the country won independence from Sudan caused hundreds of thousands of deaths between 2013 and 2018.

A tenuous peace has held between the main belligerents since then, but clashes continue among a patchwork of armed groups. Some activists say they believe a recent rise in killings is at least partly connected to the vote, which will choose leaders to succeed the current transitional government.

The shooting happened on Tuesday when the commissioner of Boma County in Pibor was returning from a visit to a village.

"The commissioner with his team went to Nyat village and on his return he was ambushed and 15 people were killed including the commissioner," Abraham Kelang, information minister of Greater Pibor Administrative Area, told Reuters.

Among the dead were Boma's deputy army commander, government officials and the county commissioner's bodyguards, Kelang said.

He said the attackers were suspected to be young people from the region's Anyuak community. They were also blamed for the killing last year of another county commissioner in Pibor and a security official.

Officials from Pochalla County, where the Anyuak are the majority, were not immediately available for comment.

Inhabited mostly by the Murle ethnic community, Boma County has experienced periodic violence between the Murle and Anyuak and with other ethnic groups from neighbouring Jonglei State. Some of the violence is motivated by cattle rustling.

More than 150 people were killed in late January and early February in northern and western South Sudan in conflicts between rival groups.

The United States, Britain and Norway on Tuesday called on South Sudan's leaders to take urgent steps to ensure a genuine and peaceful election.