Libyan rebels were trying to retake the north-eastern oil port of Brega on Wednesday after days of fighting for the key city, as the opposition moved closer to exporting oil from rebel-held ports, dpa reported.
Rebels had gained ground in Brega by Wednesday night, broadcaster al-Jazeera reported.
This comes after they were were pushed back early Wednesday to the city of Ajdabiya by Moamer Gaddafi's armed forces, opposition sources said.
The rebels were coming under heavy shelling some 30 kilometres outside Adjabiya, located between Brega and the rebel stronghold of Benghazi in the east, one source in Benghazi told the German Press Agency dpa.
A back-and-forth battle for Brega has raged for days, with rebels unable to securely reclaim control of the port and other coastal cities briefly held by opposition forces.
The opposition al-Manara website reported that according to eyewitnesses, Gaddafi's forces bombed an oil field in the town of Awjilah that belonged to a company that has sided with the rebels.
Awjilah is about 180 kilometres south-west of Benghazi, close to the city of Zueitina.
Sources told the German Press Agency dpa this week that the rebel- controlled Zueitina oil pipeline terminal is ready for operations and that bank accounts have been created to begin exporting oil.
The oil field belongs to the Arab Gulf Oil Company, whose officials had previously announced they would operate independently of the Tripoli-based, state-owned National Oil Company until Gaddafi is removed.
An oil tanker with a capacity of 1 million barrels reportedly arrived this week at the Marsa al-Hariga terminal near the port of Tobruk in eastern Libya, ready to mark the first export of oil from rebel-held areas of Libya since the conflict began six weeks ago.
Human Rights Watch on Wednesday called on the opposition's Interim Transitional National Council to make public their oil sales. "It should also commit to publish independent auditing reports in the future of any financial transactions associated with oil and gas licensing and sales," the non-governmental organization said.
Prior to the conflict, Libya was Africa's third-largest oil producer, exporting 1.6 million barrels a day.
Meanwhile, the state-news agency JANA reported that Gaddafi sent a letter to US President Barack Obama on Wednesday, but the contents of the letter were not made public. White House spokesman Jay Carney confirmed the letter's existence but did not reveal details, saying only it was "not the first."
It comes on the same day that former Republican congressman Curt Weldon, who met with Gaddafi in 2004, arrived on a private visit to Libya to ask Gaddafi to step down.
State Department spokesman Mark Toner told reporters in Washington that Weldon was not representing the US government and was there as a private citizen. Weldon, however, did inform the Obama administration of his intention to meet with Gaddafi, Toner said.
Earlier Wednesday, the military leader of the rebels, General Abdul Fattah Younis, confirmed having received weapons from allied countries, but stopped short of saying which countries had supplied arms.
Russian Foreign Minister Sergey Lavrov on Wednesday warned NATO against arming Libyan rebels, according to the news agency Interfax. "That would break the UN resolution" authorizing the no-fly zone over Libya, he said.
Libyan rebel leaders, including Younis, said NATO was not moving quickly enough to destroy Gaddafi's attack units.
"Sadly, NATO has let us down. Myself and my officers called the NATO officers and gave them the targets that if struck will protect the civilians. But the NATO coalition has not given us what we want," Younis told satellite broadcaster al-Aan about the ongoing NATO airstrikes on Gaddafi's forces.
NATO on Wednesday rejected claims that the alliance had been too slow to attack Gaddafi's forces.
"The pace of NATO operations continues unabated," said a NATO official, who was not authorized to speak on the record.