04/18/2012 14:37 GMT

by Ian Timberlake

KHARTOUM, Sudan, April 17, 2012 (AFP) - The South's eight-day occupation of Sudan's key Heglig oil field must end "by hook or crook", the foreign ministry said on Wednesday, as international pressure mounted to pull the rivals back from the brink of all-out war.

Sudan is pursuing both military and diplomatic measures to get South Sudan out of the area, Omar Dahab, head of the ministry's crisis team, told a news conference.

"Military steps are underway ... and they are calculated measures," he said. "At the same time, they are taking into consideration the diplomatic and good offices efforts regarding the ending of the occupation.

"We have to end the occupation by hook or crook, by either way."

Sudan's military has released virtually no information about the situation on the ground but South Sudan has vowed to hold its positions in Heglig, despite air strikes.

Clashes broke out last month in the Heglig area and escalated last week with waves of aerial bombardment hitting the South and Juba's seizure of Heglig on April 10.

The United Nations, the United States and the European Union have criticised the South's occupation of Heglig, the north's most important oil field, equally denouncing Sudanese air strikes against the South.

There are widespread fears that the fighting, which began with skirmishes in the same area in late March and intensified last week, will spread.

It is already the worst since South Sudan won independence in July after a 1983-2005 civil war which killed two million people.

Sudan has vowed to react with "all means" against the Heglig invasion, which many in Khartoum say occurred with surprising ease and has been called a humiliation for the military.

On Tuesday, the UN Security Council discussed possible sanctions against Sudan and South Sudan in a bid to halt a wider war.

It again demanded that South Sudanese troops pull out of Heglig and that the north should end cross-border air attacks, said Susan Rice, the US ambassador and council president for April.

For its part, the African Union renewed its demand for both sides' forces to leave the region.

Air strikes have killed several South Sudanese civilians and earlier this week damaged a UN peacekeeping camp in the South's Unity State.

Rice said the council discussed ways to leverage its influence "to press the parties to take these steps and included in that a discussion potentially of sanctions".

The two Sudans are locked "in a logic of war," with hardliners controlling both countries, international peace envoys told the council.

Although South Sudan disputes it, Heglig has been internationally recognised as being part of Sudan.

A US envoy is expected in Khartoum on Thursday after a meeting in the South's capital Juba with President Salva Kiir.

Princeton Lyman, the special envoy on Sudan and South Sudan, will "essentially stress the same message, which is that we need an immediate and unconditional cessation of violence, and we need both sides to get back to the AU process," State Department spokesman Mark Toner said.

He was referring to talks on a variety of protracted disputes brokered by the African Union. Sudan pulled out of those talks after the Heglig attack.

The US has urged South Sudan to withdraw but, despite its heavy reliance on US aid, Juba has remained defiant.

Both sides reported a deadly skirmish on Tuesday around their borders just outside the contested Abyei area, about 170 kilometres (105 miles) west of Heglig.

It is the first reported fighting in the area since the Heglig invasion and the Sudanese Media Centre, which is close to the security apparatus, alleged it aimed to affect Sudanese military plans to recapture the oil field.

Analysts say they have no idea who began the latest fighting in a region where Sudan has tightly restricted the movement of journalists, diplomats and foreign aid workers.

South Sudanese President Salva Kiir has set conditions for a withdrawal from Heglig, among which is that Sudanese forces occupying Abyei must withdraw.

Abyei was to hold a referendum in January last year to determine whether it would be controlled by Khartoum or Juba but the vote was stalled and Sudanese troops seized the area in May.

strs-it/al