New York (AFP) - Argentina's new government has offered $6.5 billion to settle its long debt battle with "holdout" creditors, the government and a US mediator said Friday, declaring a breakthrough to the impasse.

The dispute and the US court case around it has roiled global sovereign debt markets while deeply hampering Argentina's ability to access international capital to fund its economy.

Two of six major holdout creditors have accepted the deal, which includes about a 25 percent "haircut" on their claim, while four have not done so yet, according to the government.

The offer was made in New York talks with hedge funds and other creditors who had demanded full repayment of about $9 billion on bonds the country defaulted on 15 years ago.

"This litigation has gone on for nearly 15 years since the original Argentine default of 2001, and the proposal by Argentina is an historic breakthrough," said mediator Daniel Pollack.

If the offer is accepted and all the conditions met, he said, it "will allow Argentina to return to the global financial markets to raise much-needed capital."

He said that the proposal was subject to two conditions: That it gains approval by Argentina's Congress and that it also brings the release of the New York federal court's injunction, which prevents Buenos Aires from paying any other creditors outside the so-called holdout group.

The holdouts, whose decade-long court battle against Buenos Aires was led by two New York hedge funds, are a minority class of creditors which refused to go along with the restructuring of the country's debt after it defaulted on about $100 billion in 2001.

Buenos Aires said it was offering the creditors roughly 75 percent of what they were claiming, covering the face value and accumulated interest on the bonds.

- 'Vultures' -

The offer comes days after the government of President Mauricio Macri, who took office in December, reached a deal to pay Italian bondholders $1.35 billion to settle their $2.5 billion in claims dating back to the default.

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Macri's predecessor Cristina Kirchner had refused to pay the holdouts.

She insisted that they should have joined in with the 93 percent of the country's creditors which accepted a significant reduction in what they were owed to help the country restructure its finances.

Kirchner branded the hedge funds which led the holdout claims, NML Capital, a unit of Elliott Management, and Aurelius Capital Management as "vultures," saying they bought up Argentine debt cheaply around the time of the default and then refused to take part in the restructuring in order to reap huge profits.

Both hedge funds had yet to say whether they accept or reject the new offer by Buenos Aires.

The funds which accepted the offer were Montreux Partners and Dart Management, according to the government.

Pollack said more work "remains to be done" on the proposal and that he hoped that the country would be able to resolve its differences with the other main parties to the case.

He said he had spoken to Macri and Argentine Economy Minister Alfonso Prat-Gay, who both confirmed they "stand solidly behind this proposal."

"Both have shown courage and flexibility in stepping up to and dealing with this long-festering problem which was not of their making," he said.

Nevertheless, the condition that the deals gain the approval of the Argentine Congress could become a sticking point. Macri took power without a majority in the legislature, and Kirchner's block remains powerful, though it showed signs of fragmenting this week.