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One of the deadliest civil wars in recent history came a few steps closer to ending on Wednesday, as the presidents of Sudan and South Sudan sat down to talk through years of disputes and disagreements.

Omar al-Bashir and Salva Kiir discussed starting trade and cooperation, especially over oil exports and border disagreements, during a state visit to Khartoum.

"One [area of discussion] is the resumption of oil in former Unity State," said South Sudan's minister in the office of the president, Mayik Ayi Deng.

"Second, they are going to discuss border issues concerning trade between the two countries; and third they are going to discuss the issues concerning trade itself."

The vast majority of South Sudan's accessible oil deposits are located in its northern Unity state, but pipelines have remained inactive for at least two years due to the country's ongoing civil war.

The majority of these exports have historically flowed north through Sudan, but these pipelines mostly stopped due to a disagreement over Khartoum's export taxes. An agreement over the future of oil exports is to be discussed between the two presidents on Thursday.

This week's summit meeting follows a warning last week from the United States ambassador to the United Nations, Nikki Haley.

Haley reportedly told President Kiir during a visit to Juba that Washington was reconsidering its continued investment in South Sudan, totaling almost $11 billion.

"The hate and violence… has to stop," Haley said.

Washington has placed increased pressure on both sides to end their fighting via proxy rebel armies in recent months.

One of Washington's key demands over the lifting of economic sanctions on Sudan in October was an end to its support for rebel forces in South Sudan.

According to a statement from President Kiir on Tuesday, Wednesday's talks were aimed at the "establishment of stable relations" through discussion over disputed issues.

Juba's Eye Radio reported that defence ministers held a co-operation meeting on Wednesday to discuss border issues and security cooperation.

The ministers reportedly met to agree on an officially agreed border line and the future of the disputed Abyei region.

Relations have remained poor between the two countries since South Sudan seceded in 2011. The Sudanese government has repeatedly accused Juba of supporting rebel groups in its southern regions, while the South Sudanese army has made similar claims over Khartoum's support of its own rebel groups in the north.

A bitter civil war in South Sudan has caused almost two million civilians to leave the country, with around half a million civilians seeking refuge in Sudan, the UN reports.

A series of man-made disasters has created one of the region's worst famines and has allowed disease, including cholera, to spread rapidly.

It is hoped that President Kiir's visit to Khartoum, his third ever since 2011, will help alleviate the causes of this conflict as the two historic enemies discuss economic co-operation.

A recent report from The Sentry found that military and political leaders had exploited sectarian hatred to further extend the civil war. An analysis of leaked bank records found that a large number of senior ministers had become inexplicably wealthy through the sale of weapons.