A delegation of Yemen's Houthi rebels left the capital Sana'a for Sweden on Tuesday, accompanied by the United Nations' special envoy to Yemen, Martin Griffiths, to take part in expected peace talks aimed at ending the nearly four-year-long conflict.

Rebel spokesman Mohammed Abdul Salam wrote on Twitter that the delegation left for Sweden on board a Kuwaiti plane.

‘We will spare no effort to make the consultations succeed, to bring peace, end the war of aggression and lift the siege. Our hands are stretched out for peace,’ Abdul Salam said.

‘At the same time, we call on the army, security and the popular committees to be vigilant against any escalation,’ he added.

A source at Sana'a airport told dpa the delegation was accompanied by Griffiths.

The UN envoy arrived in Sana'a on Monday in a bid to pave the way for peace talks, which come after nearly four years of war that have led to displacement, food insecurity, outbreaks of cholera and diphtheria across the country.

A previous attempt by Griffiths to hold UN-sponsored talks in Geneva collapsed in September when the rebels failed to appear.

The UN considers Yemen the world's worst humanitarian crisis, and has repeatedly warned of a looming famine.

Meanwhile, the Saudi-backed government's delegation is expected to arrive in Sweden on Wednesday, according to a source affiliated with the government.

The source added that negotiations are expected to start on Thursday.

The government delegation will be led by Foreign Minister Khaled al-Yamani.

Saudi Arabia and the United Arab Emirates are leading a Sunni coalition that began an air campaign against the Houthi rebels in Yemen in March 2015.

The coalition, which has been repeatedly blamed for civilian deaths, was formed a few months after the Iran-backed Houthis took over the capital Sana'a and other parts of Yemen in late 2014.

The expected talks come after the coalition approved the transfer of 50 wounded Houthi rebels to the Omani capital Muscat for treatment on Monday.

Also on Monday, the Houthi rebels said they were informed by Griffiths that the coalition had signed a prisoner swap deal, which the Houthis signed in November.

‘Today we completed the procedures and received a signed copy of the agreement. This will be the first step to end this humanitarian issue,’ said Abdul Qader al-Mortada, the head of the rebel-affiliated National Committee for Prisoners Affairs.

The negotiations in Sweden are expected to focus on opening Sana'a airport, which has been closed for commercial flights since August 2016 due to restrictions imposed by the Saudi-led coalition. The talks will also focus on lifting the Houthi-imposed siege on Yemen's south-western city of Taiz.