KUWAIT (Reuters) - The United Nations and world powers sought on Tuesday to persuade Yemen’s Houthis to send representatives to peace talks in Kuwait as a shaky truce teetered near collapse, delegates said.

A Houthi militant mans a checkpoint in Yemen's capital Sanaa April 18, 2016. REUTERS/Khaled Abdullah

Houthi negotiators have stayed put in the capital Sanaa, which their movement holds, demanding a ceasefire that began on April 10 be fully observed before they travel for the talks originally planned to start with representatives of President Abd-Rabbu Mansour Hadi’s government on Monday.

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

A failure of the talks is likely to stoke fighting between the Iran-allied 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.

An advisor to the U.N. delegation in Kuwait said the Houthis had been “very positive” until two days ago and had agreed with envoy Ismail Ould Cheikh Ahmed on almost everything.

“They have since completely changed and this has caused a shock),” the aide, who asked not to be identified, told Reuters.

The envoy was now working with the Houthis and the government to iron out the problems.

U.N. Secretary-General Ban Ki-moon appealed to all Yemeni parties to engage with Ould Cheikh Ahmed “so that talks can start without further delay”.

A Western diplomat said the Chinese ambassador to Yemen delivered a message from the five permanent members of the U.N. Security Council to the Houthis urging them to attend the talks.

“We understand your concerns but you need to carry your worries to Kuwait and put them at the table,” the diplomat said, quoting the message.

Hadi’s government has ordered its delegation to stay put in Kuwait while the United Nations sought to persuade the Houthis to join the talks.

Residents in Marib province east of Sanna meanwhile reported intensified fighting after troops loyal to Hadi arrived on Monday after training in Saudi Arabia

Fighting was also taking place in Taiz in southwestern Yemen despite the presence of ceasefire monitors, while Saudi-led warplanes flew over the Yemeni capital.

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

HUMANITARIAN DISASTER

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 Qaeda and Islamic State 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.

The 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 the Houthis say they were still unable to curb continued violations of the truce.

Houthi spokesman Mohammed Abdul-Salam said on Monday the movement had long been ready for a dialogue to bring peace to Yemen and stability to the entire region, but the violence had not stopped with the ceasefire.

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 Houthi leader, criticized the U.N. envoy, accusing him of presenting contradictory drafts for peace talks. He said in a Facebook posting that his group was ready for peace “at any venue and at any time” as soon as the fighting stops.