South Sudan’s government is failing to push through a peace deal, the country’s main opposition has said, calling for a six-month delay in the formation of a unity administration.

The spokesman for former rebel leader Riek Machar said he did not believe he would be able to join a unity government on November 12 – a deadline agreed in September after months of talks, broken ceasefires and pressure from the United Nations, the United States and regional powers.

“It’s not rocket science that the government in Juba lacks political will to implement the peace deal,” Puok Both Buluang, Machar’s spokesman, said.

Buluang called on the government to release funds it had agreed to spend on rolling out the accord. The extra six months would “give room” for resolving issues, he added.

Speaking later at a public event, President Salva Kiir did not directly address the comments from Machar’s camp.

Kiir said all parties to the agreement had committed to forming the unity government on November 12 and the international community expected that to happen.

“I want to welcome (the opposition) and forget all the bitterness,” Kiir said.

There was no immediate comment from other countries who helped broker the accord.

US officials said this month they would not accept more delays and might impose sanctions if deadlines are not met.

Al Jazeera’s Hiba Morgan, reporting from neighbouring Sudan said external mediators might have to intervene if the deadline is to be met.

“Machar is saying the security arrangements which were included in the peace deal that was signed in Khartoum are not yet in place. According to that agreement, 83,000 troops from all sides are supposed to be merged together to form a unified army,” Morgan said from the capital, Khartoum.

“IGAD, the regional body, is saying it is up to the mediators to decide whether there should be another extension to the deal. The mediators were Uganda and Sudan. Officials in Khartoum have told us they are speaking to Kiir on the latest development,” she added.

South Sudan split from Sudan in 2011 after decades of war, then plunged into its own conflict at the end of 2013 when Kiir had a fallout with Machar, his then-vice president.

Troops loyal to both men clashed in the capital Juba that December and ethnically charged fighting spread, shutting down oil fields, forcing a third of the country’s population from their homes and killing more than 400,000 people.

The peace deal has stopped the fighting but South Sudan’s government has said it does not have the finances to fund disarmament and the integration of rebels into the army.

So far, it has allocated $10m of the pledged $100m, according to the international body monitoring the ceasefire.

Both sides have also disagreed on details of the deal, including the number of states South Sudan should have. Under the accord, they have agreed to hold elections after a transition period of three years.

A UN Security Council delegation visited Juba earlier this month in an attempt to persuade the two sides to solve their remaining disputes over the pact.

It is unlikely that fighting will resume after the missed deadline, said Alan Boswell, a senior analyst with Brussels-based think-tank International Crisis Group.

This is largely because most of the international community is now urging both sides to agree on a new plan by the deadline in order to salvage the deal, he said.