Talks on a U.N.-sponsored prisoner swap in Yemen’s war could drag on for months if the Saudi-backed government denies the existence of thousands of Houthi fighters in captivity, the Iranian-aligned Houthis said on Thursday.

In two rounds of talks in the Jordanian capital Amman, the warring parties have been hammering out details of the prisoner exchange they agreed last December as a confidence-building gesture at the first major peace talks of the nearly four-year-old war.

The United Nations is pushing for the swap and for a peace deal in the country’s main port city of Hodeidah as part of stepped up efforts to end the nearly four-year conflict that has left 15.9 million people facing severe hunger.

Delegates to the talks have been struggling to come with a final list of detainees after verifying an initial one they exchanged in Sweden that had around 15,000 people.

Abdul Qader Murtada, who heads the Houthi delegation, said the government side had accounted for only a tenth of a total of 7,500 of Houthi prisoners held in the United Arab Emirates and Saudi Arabia.

“If the other side remains in its intransigent position of denying the presence of our prisoners the talks will drag on for months,” he told Reuters on the sidelines of the current round of talks, which began on Tuesday.

The Houthis have in turn recognized only 3,600 from an original list of 9,500 names submitted by the government side of their detainees, saying over 4,000 names were either fake, duplicate names or of prisoners who had been released, he added.

Murtada also said they had “tens” of captive Saudi military personnel in their jails, some of whom were high ranking and whose release would only take place if all their prisoners were released.

“The Saudis are tied to the fate of the Yemenis as a whole and we reject entering into negotiations with them except over a deal that involves all our prisoners,” he said.

The Yemeni government’s backers have not commented on the course of the prisoner swap talks.

Saudi Arabia and the United Arab Emirates - leaders of a Western-backed coalition battling the Houthis to restore President Abd-Rabbu Mansour Hadi’s government - want to exit a costly war that has dragged on for nearly four years. They have endorsed the U.N. push to reach a peace deal.

The discussions over the swap, which would be conducted via the Houthi-held Sanaa airport in north Yemen and the government-held Sayun airport in the south, have also included returning remains of dead fighters from both sides.

AFP.