Kuwait: The UN envoy to Yemen sought on Tuesday to persuade Yemen’s Al Houthi group to send representatives to peace talks in Kuwait as a truce declared this month teetered on collapse, delegates said.

An adviser to the UN delegation in Kuwait said Al Houthis had been “very positive” until two days ago and had agreed with envoy Esmail Ould Shaikh Ahmad on almost everything.

“They have since completely changed and this has caused a shock (to Ould Shaikh Ahmad),” the aide, who asked not to be identified said. The envoy was now working with Al Houthis and the government to iron out the problems.

Al Houthi negotiators have stayed put in the capital Sana’a, demanding a ceasefire begun on April 10 be fully observed before travelling for the talks with envoys from Yemeni President Abd Rabbo Mansour Hadi’s government in Kuwait.

Al Houthis have also rejected a proposed agenda that stipulates they hand over heavy weapons and withdraw from areas they controls before a new government comprising all Yemeni forces is formed.

Any failure of the talks is likely to stoke intensified fighting between the Iran-allied Al Houthis and their ally, former President Ali Abdullah Saleh, on the one side and Hadi supporters, backed by a Saudi-led Arab coalition, on the other.

Residents in Marib reported intensified fighting in the province east of Sana’a after fresh troop reinforcements loyal to Hadi arrived on Monday after training in Saudi Arabia. They also reported more fighting in Taiz in southwestern Yemen, despite the presence of ceasefire monitors, while Saudi-led war planes flew over the Yemeni capital.

Delegates representing Hadi’s government have threatened to leave Kuwait, accusing Al Houthis of trying to impose new conditions on the talks. Officials said delegates were meeting at the emir’s palace to decide on their next move.

Al Houthis have observed a period of calm along the border with Saudi Arabia and exchanged prisoners with Riyadh, paving the way for Ould Shaikh Ahmad to draft a broad outline for the talks, which were due to start on Monday.

The United Nations says the Yemen war has killed more than 6,200 people and displaced millions of people in the poorest country in the Arabian Peninsula.

Al Qaida and Daesh have also exploited the war to widen their influence and gain more supporters in a country next door to Saudi Arabia, the world’s top oil exporter.

Al Houthis complain that Hadi’s forces are trying to exploit the truce to try to make gains on the ground in several provinces, while war planes from the Saudi-led alliance continued to fly over areas held by the group.

Teams of joint ceasefire monitors have been deployed in some areas, but Al Houthis say they were still unable to curb continued violations of the truce.

Al Houthi spokesman Mohammad Abdul Salam, in a Facebook posting on Monday, said his group had long been ready for a dialogue to bring peace to Yemen and stability to the entire region.

“Unfortunately, and since the April 11 (ceasefire), aggression had not stopped,” he said.

Abdul Salam said one of the committees set up to monitor the ceasefire in the northern Al Jawf province had had a lucky escape from an air strike by the Saudi-led coalition.

Abu Malek Al Feeshi, another prominent Al Houthi leader, lashed out at the UN envoy, accusing him of presenting contradictory drafts for peace talks. He said in a Facebook posting that his group was ready for peace talks “at any venue and at any time” as soon as the fighting stops.