GENEVA — The Syrian opposition will seek an extension of the current round of U.N.-hosted peace talks underway in Geneva, saying Wednesday it needed more negotiating time.

Salem Meslet, an opposition spokesman, said it was “not right” that this round is expected to last just four days. The opposition needed time to prepare its response to a “paper” presented by U.N. special envoy Staffan de Mistura on Tuesday, when the sixth round of the talks started.

Meslet, who spoke at a demonstration outside of the U.N. Geneva compound led by female relatives of prisoners held in Syria, said the proposal involved “the constitutional frame” for an eventual transition period in Syria.

Later Wednesday, President Bashar Assad’s top envoy met separately with de Mistura inside the compound.

Meslet said it was a “big question mark” when de Mistura proposed the unusually short four-day round, adding: “We request a longer time.”

He said negotiations to end the six-year conflict needed to take place “without any rest, without any break.” Alluding to backers of Assad — Russia and Iran — he said the country’s future should be decided “in Syria — not in Moscow or Tehran.”

In a bid to “avoid any constitutional or legal vacuums at any stage during the political transition process being negotiated,” the U.N. envoy has suggested forming a team of technocrats to lay the foundations for the future drafting of a new constitution.

The proposal, according to a document first released by the Al Jazeera news channel, foresees the creation of a “consultative” team which will be headed by experts from de Mistura’s office and include qualified representatives from both the Syrian government and opposition.

Representatives of the Syrian opposition on Wednesday confirmed the authenticity of the document to The Associated Press.

Tuesday’s start of talks in Geneva were overshadowed by U.S. accusations that the government in Damascus carried out mass killings at a prison near the Syrian capital and then burned the victims’ bodies in a crematorium. Assad’s government rejected the claims, describing the allegations as “lies” and “fabrications.”

The allegations come at a time when the Trump administration is weighing its options in Syria, where an estimated 400,000 have been killed and half the population displaced by the 6-year-old civil war.

Last month, the U.S. fired cruise missiles on a government air base after accusing Assad’s military of killing scores of civilians with a sarin-like nerve agent.