A rebel stands at the front line outside Brega in eastern Libya, April 1, 2011. [Photo/Aagencies]

TRIPOLI - Heavy fighting between Libya's rebel forces and government troops continued in the eastern oil town of Brega on Sunday.

Brega is one of those cities which have been taken and retaken again and again by rebels and government forces after the Western coalition began air strikes against Gaddafi's forces.

The town is of key importance: It, along with the eastern town of Ras Lanuf, produces the lion's share of Libya's 1.5 million oil barrels of daily exports, which have been radically affected by the uprising since February 15.

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Also on Sunday, the Western military alliance said in its daily report that NATO carried out 70 airstrikes over Libya Saturday.

NATO aircraft are enforcing a no-fly zone and protecting civilians by conducting airstrikes in Libya, while the alliance's naval vessels are patrolling the Mediterranean to implement an arms embargo.

NATO aircraft conducted 184 sorties on Saturday, including 70 "strike sorties," the alliance said.

Strike sorties "are intended to identify and engage appropriate targets, but do not necessarily deploy munitions each time," NATO explained.

Since the beginning of the NATO-commanded mission, code-named Unified Protector, since Thursday, a total of 547 sorties and 218 strike sorties have been conducted.

Twenty-one naval vessels under NATO command are patrolling the central Mediterranean to enforce an arms embargo against Libya, NATO said in a report.

Four vessels were hailed Saturday to "determine destination and cargo. One boarding was required," the report said.

Meanwhile, Tunisia's state-run TAP news agency reported that Libya's Deputy Foreign Minister Abdul-Atti Al-Ubaidi had crossed the Libyan border into Tunisia Sunday.

Libyan Foreign Minister Mussa Kussa took the same route when he defected last month, but the purpose of Al-Ubaidi's trip was unclear.

The agency said the visit by Al-Ubaidi, who is responsible for European Affairs, was not official.

TAP said Al-Ubaidi was heading for Djerba airport, but did not disclose where he was flying to.

As the Western-led air strikes continue, the risk of civilian casualties is increasing, and more and more people are becoming homeless.

UN Humanitarian Coordinator for Libya Rashid Khalikov on Sunday called on the international community to continue to provide assistance to refugees stranded on Libyan borders.

The UN official said at a press conference held in Tunisia's capital Tunis that the situation at the Tunisian-Libyan border point of Ras El Jedir was "under control," praising the efforts of Tunisia's military authorities and the people in helping refugees cross the border.

Some 400,000 refugees have fled the violence in Libya since February, he said, adding that if more people remain stranded for a long time on borders such as Ras El Jedir, "more problems are likely to emerge in the refugee camps, as well as weighing negatively on the economies that host them."

Khalikov stressed that it is important to "intensify efforts to swiftly evacuate the refugees," indicating that the UN has launched an appeal to collect $310 million in donations to help those on the Tunisian-Libyan border, following a previous call to collect $160 million.

Talking about the situation in unrest-ridden areas in Libya, the UN official warned of further degradation in the absence of basic food and medical assistance. He also called on the sides concerned to respect international humanitarian law and human rights accords to guarantee the security of civilians.