For the second day in a row South Sudan's rebel leader failed to make his much-anticipated return to the capital, Juba, after more than two years of war.

Riek Machar, a former rebel leader turned deputy president who was fired, became a rebel leader again and has now fought his way back to the vice presidency, failed to appear in Juba as expected on Monday or Tuesday.

Speaking to reporters staking out Juba's airport since early Monday, rebel spokesmen William Ezekiel said on Tuesday afternoon that unspecified "issues relating to logistics" were to blame for the latest delay. He was unable to say when Machar might now arrive.

"He is going to come. But when?" Ezekiel said. It was unclear whether the question was rhetorical.

"We will update you," he added.

However, South Sudan's information minister Michael Makuei said the government had blocked Machar's flight because he wanted to bring "machine guns and laser-guided missiles" as well as additional troops in contravention of the peace agreement.

Makuei said Machar had now "called off his arrival indefinitely".

"I will only believe it when I see him at Juba airport," he said.

Machar's homecoming and subsequent swearing-in as vice president are seen as important steps towards implementing a floundering August 2015 peace deal that has so far failed to end the country's civil war, sparked by a wrangling for power between Machar and President Salva Kiir.

Both sides continue to insist they are committed to peace while offering little evidence to back their claims.

The conflict characterised by extreme brutality and human rights violations has killed tens of thousands, forced millions from their homes and split the country along old ethnic fissures.

Machar is believed to be either in his tribal stronghold of Pagak in the east of the country or in Gambella, Ethiopia, where there is an airstrip large enough to land a plane to carry him and his entourage to Juba.

Various rebel officials have given differing explanations for the delays, with some citing difficulties in getting Machar's bodyguards' weapons across the border while others blamed bad weather. Other sources suggested the presence of Machar's UN and US sanctioned chief of staff, Simon Gatwech Dual, in the rebel travelling party, was the hitch.

As news of Machar's latest no-show broke on Tuesday afternoon at Juba airport, dancers put away their finery, rebel soldiers roared off in their pickup trucks and a woman walked away carrying a box of speckled doves that were due to be released as a symbol of peace.