The armies of north and south Sudan clashed on the country\'s tense border on Friday, near the flashpoint Abyei region, the southern army spokesman said, less than a month before southern independence. The United Nations confirmed that there had been an exchange of heavy artillery fire coming from the direction of the Kiir, or Bahr al-Arab river, which runs through the Abyei region, and where similar clashes reportedly took place on Wednesday. \"This morning we received a report that the SAF (Sudanese Armed Forces -- northern army) were trying to move southwards into Warrap state,\" in south Sudan, Philip Aguer, the spokesman of the Sudan People\'s Liberation Army of the south, told AFP. \"There was fighting between Abyei and Agok (45 kilometres south)... But our forces repelled them and drove them back towards Abyei,\" he said, adding that the northern army had deployed all along the north-south border. The northern army spokesman could not immediately be reached for comment. Northern troops overran the bitterly contested Abyei region on May 21, in response to an attack on a convoy of SAF troops and UN peacekeepers, in which at least 22 northern troops were killed and which was blamed on the south. The move prompted around 113,000 people, mostly pro-southern Dinka Ngok farmers, to flee to the south, according to the latest UN estimates. Aguer said on Friday that five SAF soldiers had been killed and seven SPLA troops wounded in the fighting that broke out two days ago, near the river, but the SAF spokesman denied the northern army\'s involvement in any clashes with southern troops. \"The SPLA has to find out who is fighting them south of the Bahr al-Arab,\" Sawarmi Khaled Saad told reporters. Abyei is the most sensitive and intractable of a raft of issues that the two future states are struggling to resolve ahead of the south\'s formal declaration of independence from the north on July 9. But very little progress appears to have been made on these issues, despite Sudan\'s two presidents agreeing \"in principle\" earlier this week to withdraw Sudanese troops from Abyei and deploy Ethiopian peacekeepers. The renewed violence in Abyei, and in nearby South Kordofan, threatens to poison north-south relations ahead of south Sudan\'s full international recognition next month.