(Adds U.N. sanctions threat, Sudan backing AU road map)
* South Sudan seized oilfield briefly last month
* Sudan says oil started pumping on Monday
* Khartoum accuses foreigners of taking part in oil field destruction
HEGLIG, Sudan, May 2 Sudan said on Wednesday the Heglig oilfield, scene of intense fighting with South Sudan last month, has been repaired and has started pumping the oil that is the lifeblood of the north's economy.
The two countries have been embroiled in weeks of fighting along their 1,800 km (1,200 mile) border, threatening to tip the region, which sits on one of Africa's most significant oil deposits, into a full-blown conflict.
The United Nations Security Council approved a resolution that threatens both countries with sanctions if they do not stop fighting and resume negotiations within two weeks, as demanded by the African Union.
China, which has close trade relations with both countries, and Russia supported the resolution after several days of negotiations with council members during which they resisted the Western push for a threat of sanctions.
"The fighting must stop, and stop now," the U.S. Ambassador to the United Nations Susan Rice told the council.
At the same time, Sudan said it agreed "in principle" with an African Union plan to end the crisis with the south.
The AU demanded on April 24 that Sudan and South Sudan resume talks within two weeks, warning both it would issue its own binding rulings if they fail to strike deals on a series of disputes within three months.
The AU has spearheaded mediation efforts between the two foes in the past with the backing of the United Nations, the United States and other major powers. South Sudan committed to the AU road map last month.
South Sudan's army, the SPLA, said it killed 27 Sudanese army soldiers in a clash in Unity state on Tuesday.
But despite the persistent clashes in the border region, the two countries have stopped short of all-out war, with their positions broadly the same as before the south seized Heglig.
Sudan accused South Sudan of launching several attacks over the past week on its territory. It said the SPLA had occupied a border village in Bahr al-Arab as well as the disputed areas of Kafn Dubai and Kafya Kenji.
South Sudan seized the contested Heglig oilfield last month before withdrawing shortly afterwards. The field is vital to Sudan's economy because it produced almost half of the country's output of 115,000 barrels per day.
"This oilfield was producing 55,000 barrels per day," Sudanese Petroleum Minister Awad Ahmed al-Jaz said at the oilfield, accompanied by oil engineers and military officers.
"Now as we said ... we plan to produce more than that, besides the production of other oilfields which will follow," he said, as he opened one the oil valves.
Jaz said the oilfield had started pumping oil at 10 p.m. (1900 GMT) on Monday. He did not indicate how much Heglig was currently producing.
"We can say the oil has now reached the Khartoum refinery."
Sudan lost three-quarters of its output when South Sudan became independent in July last year.
Both countries are at loggerheads over how much the southern landlocked nation should pay to export its crude through the north. The conflict has shut down nearly all oil production in the region, strangling both countries' oil-dependent economies.
In January, South Sudan shut down its entire output of 350,000 bpd to stop Khartoum taking some oil for what it calls unpaid transit fees.
Satellite images showed a key part of the oil infrastructure in Heglig was destroyed in the fighting. An earlier trip to Heglig showed damaged pipelines that were leaking oil.
On Wednesday, reporters saw pipelines that had been repaired, but which still bore the effects of damage.
Jaz said the power plant as well as rooms that manage the collecting, refining and storage of the oil had been damaged.
"Those who came here and saw the damage said that the repairs could not be completed in six months," Jaz told reporters taken on an official trip to the oilfield.
"Those who were optimistic suggested it would take four months to repair the damage. But the repair only took one week."
Jaz said four foreigners, whom Khartoum said they arrested on Saturday for illegally entering Heglig and for being spies for the SPLA, had "participated in the destruction".
The four, a Briton, South African, Norwegian and South Sudanese, are U.N.-affiliated workers.
The United Nations rejected the accusations.
"All four personnel were carrying out formal demining activities in Paryang, in Unity State," a spokeswoman for the U.N. mission in South Sudan, Josephine Guerro, said.
Heglig is operated by Greater Nile Petroleum Operating Co (GNPOC), a consortium of Chinese, Malaysia, Indian and Sudanese companies. Parts of the border area around the Heglig field in Block 2 are still in dispute.
South Sudan has agreed to an immediate end to hostilities in accordance with an African Union road map, which is meant to bring the former civil war foes back to the negotiating table.
But fighting along the border has continued.
The SPLA's spokesman, Philip Aguer, said the ground attack in Hofra on Tuesday, had later been accompanied by air strikes by a Sudanese Antonov and MiG-27 fighter jets.
"The SPLA killed 27 SAF soldiers, including a major that was commanding the force," Aguer said on Wednesday. "(The SPLA) ... captured five trucks mounted with heavy machine guns. They fled towards Heglig."
Sudan's army spokesman did not answer phone calls to verify the SPLA's claims.
Limited access to the remote border areas make it difficult to verify the often contradictory statements from both sides. (Additional reporting and writing by Yara Bayoumy; Editing by David Clarke and Giles Elgood)