UNITED NATIONS — The United States will press the U.N. Security Council in a meeting this afternoon to permit the unfreezing of $1.5 billion in Libyan assets to pay for humanitarian aid, fuel and salaries for international aid agencies, as well as for a post-Gaddafi interim government, according to Security Council diplomats.

The U.S. proposal to release a portion of Moammar Gaddafi’s billions faced opposition this week from South Africa in a U.N. committee on Libyan sanctions. Proposals in the sanctions committee, which works by consensus, require the support of all 15 council members to be approved.

South Africa has not publicly explained its reason for opposing the American initiative. But South African has expressed reservations about the role of the United States and Europe in assisting the Libyan rebels’ effort to overthrow the Gaddafi regime. South Africa has focused its diplomatic efforts on pursuing a negotiated settlement to the conflict.

South Africa’s position on Libya has drawn sharp criticism from human rights advocates, including Human Rights Watch, which has faulted one of Africa’s most vibrant democracies for providing diplomatic cover to some of the continent’s most brutal dictators, including Zimbabwean leader Robert Mugabe.   

In an effort to overcome South African objections, the United States insisted the issue be put before the Security Council, where the measure would require only nine votes to pass, this afternoon. If South Africa doesn’t yield, the United States would press for a vote Thursday or Friday, according to a Security Council diplomat, who spoke on condition of anonymity.

The U.S. proposal is broken into three parts, the official said. About $500 million would cover some of the costs of a U.N. humanitarian appeal, and would be used to fund humanitarian agencies operating in Libya. Another $500 million would pay for fuel, which is in short supply, for electrical plants, desalinization plants and hospitals. And the remaining $500 million would be placed in the so-called Temporary Financing Mechanism, which was established by members of the Libya Contact Group, to pay for salaries of functionaries in a future Libyan government.

Hours before the meeting, South Africa agreed to partially lift its hold on the U.S. proposal, freeing up about $500 million to fund humanitarian relief efforts in Libya. It continued to object to the release of an additional $1 billion for fuel and salaries.