Omar al-Bashir, the Sudanese president, has suspended an April summit with his southern counterpart following renewed clashes between the two armies on the border."The government announced that it suspended Bashir’s visit to Juba after the South Sudanese army attacked (the oil-rich territory of) Heglig,” state radio reported early on Tuesday. The two leaders had been due to meet on April 3.Comments by the South’s leader Salva Kiir that his troops had taken the northern oil centre "reflected extreme hatred to Sudan,” the official SUNA  news agency quoted Abdullah Ali Massar, the information minister, as saying.South Sudan had engaged in "deceptive and misleading acts” when it signed accords with Khartoum at African Union-led talks in Ethiopia, and when last week it invited Bashir to the summit, said Massar.South Sudan, however, blamed its northern neighbour for the latest clashes."This morning the [Sudanese] air force came and bombed....areas in Unity state,” Kiir said.‘It is a war that has been imposed on us again, but is they [Khartoum] who are looking for it,” he said.Ties between the two countries have been tense since South Sudan was carved out of Sudan in July last year as an independent nation.Al Jazeera’s Peter Greste, reporting from Juba said that oil was at the heart of the issue between the two Sudans. "There are vast oil reserves along those areas [of fighting],” he said, adding that other issues also at play include land and integrity."I don’t think either side has an appetite for war, but there is a serious risk for escalation,” our correspondent said.Ban Ki-moon, the UN secretary general, called on the two countries to end the clashes and respect the agreements on border security they had already reached, said spokesman Martin Nesirky.The two sides should "utilise to the fullest extent existing political and security mechanisms to peacefully address their differences,” added the spokesman.The proposed talks between Bashir and Kiir had been aimed at easing tensions that pushed the two countries to the brink of war as recently as early March.Both countries claim parts of the oil-rich territory of Heglig.South Sudanese army spokesman Philip Aguer said fighting was still going on and there had been casualties, though he did not have full details. But the army did not want the clashes to spiral into war, he added.