South Sudan's rebel deputy chief returned to the capital Juba on Tuesday as part of a peace deal, raising hope for the expected arrival next week of the opposition leader.

Alfred Ladu Gore, a former general and minister, spoke about peace after flying into the capital's airport.

"I am very happy to be home... our advance team came here to proclaim peace and I have come to reaffirm that peace will not be reversed," said Gore, who said it had been away for nearly two years.

"We have resolved to be together and to continue with our effort to rebuild this country. It is very important that this country must occupy its place among the free nations of the world," he said, accompanied by a delegation of around 60.

However, Gore condemned the arrest of 16 supporters who had been mobilising people to welcome him back.

"Peace means freedom to express your mind, to gather together even if it means you disagree," he said.

A 1,370-strong force of opposition soldiers and police completed their arrival over the weekend into Juba. They are to ensure security for rebel chief Riek Machar — named as vice-president in February — who is due to arrive in Juba next week.

READ: South Sudan rebel troops flown to Juba for Riek Machar security

Machar has said he will come to Juba on April 18 to form a unity government with President Salva Kiir, returning for the first time since he fled the capital in December 2013 when civil war broke out.

READ: Machar to return to Juba on April 18

The arrival of rebel leaders — especially Machar, if he comes — will be a major symbolic step forward, although many warn that the practical implementation of the peace deal will be a long and tough task.

Tensions remain high, with the rebels accusing the army of boosting troops in the capital, which should be officially demilitarised within a 25 kilometre (15 mile) radius, apart from units allowed under an August 2015 peace deal. The army denies the claims.