South Sudan’s main rebel leader arrived in the capital, Juba, for talks about a peace deal that was signed last year but whose implementation has been slow. He was accompanied by one of neighboring Sudan’s most powerful military men.

The visit, only the second since rebel chief Riek Machar fled Juba on foot three years ago, is meant to “help with issues that are arising in the peace process,” his deputy Henry Odwar said by phone. Machar, who lives in the Sudanese capital, Khartoum, has disagreed with President Salva Kiir over the implementation of the accord to end a five-year civil war that’s killed hundreds of thousands of people.

Under the deal, South Sudan is to name a transitional government and Machar will return as Kiir’s deputy, a post he held both before civil war broke out in December 2013 and when he returned in 2016. A May deadline to appoint a new power-sharing government was delayed when the opposition voiced concern over the lack of progress in security arrangements for rebel forces, which are to be integrated in the army.

The presence of General Mohamed Hamdan Dagalo, the deputy head of Sudan’s military council and commonly referred to as Hemedti, indicates that Machar now has a potent ally and that Sudan considers him crucial to the peace agreement, said James Okuk, a politics professor at the University of Juba.

“Sudan, for its own well-being, is interested that the revitalized peace process is implemented and they know that Dr Riek Machar means a lot to this cause,” Okuk said by phone.

The crisis has displaced about four million people, slashed crude production and unleashed economic chaos in the country.