The United States called an urgent meeting of the UN Security Council on Wednesday to press for an easing of Libya sanctions so that it can send $1.5 billion of humanitarian aid.
The 15-member council will meet from 3:00 pm (1900 GMT) to discuss a proposed US resolution on Libya amid growing US frustration over the blocking of special aid.
The United States first asked the committee for permission to send $1.5 billion of frozen assets to Libya's opposition transitional government on August 8, a Western diplomat, speaking on condition of anonymity, told AFP.
The US administration responded to questions from other nations but South Africa has continued to block the move on the committee, the diplomat added.
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Diplomats said South Africa wanted to wait until after an African Union summit on Thursday and Friday before taking decisions on measures to help Libya.
"Now it is urgent. This money is needed for fuel for generators in hospitals, desalination plants and other facilities where it could run out in days," said the western diplomat.
If South Africa maintains its opposition after the consultations on Wednesday, the United States will press for a full vote on easing sanctions at the Security Council on Thursday or Friday, the diplomat said.
The Security Council imposed sanctions, including freezing the assets of Libyan state entities, in resolutions passed in February and March to put pressure on Moamer Kadhafi's government.
The United States and its allies say that the UN must now quickly move to change the sanctions to help the opposition Transitional National Council, that many Western governments now recognize.
The UN special envoy to Libya, Abdul Ilah al-Khatib and Ian Martin, the leader of a UN team planning for post-conflict Libya, are in Doha holding talks with the rebel government.