An influential South Sudanese minister and opposition figure has resigned, saying a fragile peace deal was dead and calling for President Salva Kiir's unity government to leave power.

Lam Akol, agriculture minister in Kiir's administration and the leader of the opposition Sudan People's Liberation Movement-Democratic Change (SPLM-DC) party, spoke out on Monday against rebel leader Riek Machar, whose forces have clashed in recent weeks with government troops loyal to the president.

Machar, who has also been vice president, was Kiir's only real opponent in a 2010 election when the young country was still a semi-autonomous territory.

"There is no more peace agreement to implement in Juba," Akol said at a press conference in the Ethiopian capital, Addis Ababa.

"The only sensible way to oppose this regime, so as to restore genuine peace to our war-torn country, is to organise outside Juba."

After gaining independence from Sudan in 2011, South Sudan descended into civil war in December 2013. 'Fraying' unity government

Under the terms of an August 2015 peace deal, the 30 ministerial posts are split between Kiir and Machar, as well as opposition and other parties.

But, after fighting broke out again,  Machar fled the capital, and Kiir  appointed a replacement from Machar's SPLM/A (IO) party, laying bare fractures within the administration and opposition.

Akol said he was working with other opposition figures so that anti-government resistance could be "consolidated".

"Since the agreement is dead and there is no free political space in Juba, the only sensible way to oppose this regime so as to restore genuine peace... is to organise outside Juba," he said.

"The entire unity government is fraying apart at the edges. [Akol’s] departure adds another blow to a very delicate situation," Robin Sanders, a former US diplomat who has worked on issues related to South Sudan, told Al Jazeera.

Sanders said she was worried Akol’s departure could push South Sudan "towards a crisis".

"If he joins forces with Machar, then you really are on the road to a bigger fight and a bigger crisis. It is a worrying sign." Renewed clashes

At least nine people were killed over the weekend in renewed clashes between troops loyal to Kiir and troops loyal to Machar, a spokesman for Machar said on Monday.

Government military spokesperson Lul Ruai Koang downplayed the weekend clashes, saying there was "small fighting" between the SPLA and Machar's forces.

"We engaged them and they tried to put up some resistance, but at the end we overcame them and they fled to different locations," Koang said.

Koang accused the SPLA-IO of shelling government positions in Nasir town in Upper Nile state, while the opposition claimed it was the SPLA that shelled their positions.

The United States said over the weekend it had received "disturbing reports" of renewed violence in the south of the country and the United Nations is considering imposing an arms embargo.