Yemen's warring parties held a fifth day of peace talks in Kuwait on Monday after the UN envoy said "significant differences" still separate them.

A UN spokesman said the talks between the government and the Shia Houthi rebels had resumed after extensive discussions of security, political and humanitarian issues on Sunday.

"Significant differences in the delegations' points of view remain but nonetheless there is consensus on the need to make peace and to work intensively towards an agreement," UN envoy Ismail Ould Cheikh Ahmed said in a statement late on Sunday.

Negotiations on a political settlement have made no headway as the two sides are still discussing ways to consolidate a fragile ceasefire that went into effect on April 11.

The delegations have agreed to appoint two officials, one from each side, to make recommendations on how to sustain the ceasefire, the envoy said.

The government delegation has insisted that the ceasefire should include confidence-building measures, such as opening safe passages to all besieged areas and releasing prisoners.

The Iran-backed Houthis are demanding an immediate halt to air strikes that a Saudi-led coalition has been carrying out since March last year in support of President Abedrabbo Mansour Hadi.

Foreign Minister Abdulmalek al-Mikhlafi, who heads the government delegation, described the negotiations as "impotent" and accused the rebels of avoiding discussion of key issues.

Mikhlafi said on his Facebook page that the rebel delegation had backed down several times on proposals they had made.

The rebels have insisted that no ceasefire can be established without an end to coalition air strikes.

The coalition has said it reserves the right to respond to rebel violations of the ceasefire, with air strikes if necessary.

The two sides also differ on the way to tackle other key issues.

The government wants the discussions to start with the issue of a Houthi withdrawal from areas they have overrun, including the capital Sanaa, and their surrender of all heavy weaponry.

The rebels want the political process and the establishment of a national unity government to come first, sources close to the talks told AFP.

The negotiations in Kuwait opened late on Thursday after the delayed arrival of representatives of the Houthi rebels and allied forces loyal to ousted president Ali Abdullah Saleh.