Former civil war foes Sudan and South Sudan are expected to resume security talks on June 21 after clashes in their contested borderlands and rows over oil payments continue to stoke tensions. Here is a look at the contentious border areas: ABYEI: - Abyei sits on the ill-defined border between Sudan and South Sudan and is claimed by both countries. Its ownership was left undecided when South Sudan split away as an independent nation last year. Abyei\'s residents were promised a referendum on which country to join, but that vote has not materialised. - The region is a microcosm of all the conflicts that have split the region for decades, an explosive mix of ethnic tension, ambiguous boundaries, oil and age-old suspicion and resentment. - Abyei contains rich pastureland, water and, after a re-drawing of its boundary, one significant oilfield - Defra, part of a block run by the Greater Nile Petroleum Operating Company (GNPOC), a consortium led by China\'s CNPC. - Most of the permanent settlements are occupied by people from the Dinka Ngok group, part of the South\'s largest tribe. For several months a year, Abyei is also used by Arab Misseriya nomads - a well-armed group that provided proxy militias for Khartoum during the north-south war. - The Misseriya fear they will lose crucial grazing rights if Abyei is included in the South. Khartoum, keen to keep the nomads\' support, has insisted they be allowed to vote in any referendum on Abyei\'s future. South Sudan, on the other hand, says only the permanent residents of Abyei - largely the Dinka Ngok - should be allowed to vote. CURRENT STATUS: - About 3,800 Ethiopian U.N. peacekeepers are currently deployed in Abyei, which is meant to be demilitarised with a civilian administration under a U.N. peace plan. - South Sudan has already withdrawn its troops from Abyei but has kept 20 unarmed security personnel in the area. - Sudan said it had pulled its police forces from Abyei, removing a possible obstacle to more peace talks. - Sudan had seized Abyei a year ago, triggering the exodus of thousands of civilians, after an attack on a military convoy blamed by the United Nations on southern forces. - South Sudan said on June 1 it had filed a complaint against Sudan at the U.N. Security Council, asking it to impose sanctions on Khartoum over its presence in Abyei. The two countries came close to war when a border dispute in April saw the worst violence since the 2011 split. SOUTH KORDOFAN: - South Kordofan is inhabited by at least 2.5 million people with more than 100 ethnic communities; the majority population is represented by the non-Arab Nuba, together with Misseriya and Hawazma Arabs. - South Kordofan lies on the Sudanese side of the border. But the oil-producing state is also home to thousands of South-aligned fighters who sided against Khartoum during the last civil war. Sudan\'s army has been fighting rebels of the SPLM-North in South Kordofan and Blue Nile states, forcing tens of thousands of civilians to flee to neighbouring South Sudan and Ethiopia. - Fighting erupted in the state in June 2011 and spread to nearby Blue Nile in September. The U.N. refugee agency UNHCR has said 35,000 people arrived in South Sudan from Blue Nile and more were on the way, joining about 70,000 refugees already living in crowded camps. - In April global powers widely condemned South Sudan\'s seizure of Heglig oil field in South Kordofan, urging the two sides to stop fighting and return to talks. - South Sudan said Heglig, which many from the South refer to as Panthou, is its rightful territory, an assertion Khartoum hotly contests. Heglig produced about half of Sudan\'s oil output of 115,000 barrels per day (bpd) before the clashes. South Sudan withdrew in the face of international pressure. Juba said it took Heglig only in self-defence after Sudan attacked its territory from there. - South Sudan is negotiating to place Heglig in a demilitarised buffer zone run by a joint administration. BLUE NILE: - Sudan\'s Blue Nile state is home to many supporters of the South\'s dominant Sudan People\'s Liberation Movement. - Human Rights Watch said in a report in April that people in Blue Nile state are continuing to endure indiscriminate bombing and other abuses. Sudan denies the claims, which are difficult to verify independently because of the remoteness of the region and because Sudan limits access for aid groups and independent monitors. More than 100,000 people are refugees in South Sudan and Ethiopia, and another 100,000 are still displaced in Blue Nile, including groups of potentially several thousand who are stranded in remote areas. - Under the 2005 Comprehensive Peace Agreement, the deal which ended decades of civil war and, eventually, allowed South Sudan to secede, residents of South Kordofan and Blue Nile were offered \"popular consultations\" to determine their relationship to Khartoum. They have not been completed.