Yemen's warring parties held their first face-to-face meeting in nearly a week on Monday after the government delegation ended a boycott, the UN envoy said.

Ismail Ould Cheikh Ahmed said in a statement that a joint meeting was held between the two delegations which have gathered in Kuwait and later he met with them separately.

He urged the two parties "to exert all efforts to achieve a sustainable solution for the sake of easing the suffering of Yemenis".

"Any delay, retreat or boycott will take us backward and slow down the solution Yemenis are waiting for," Ould Cheikh Ahmed said.

The troubled negotiations which began on April 21 broke off last Tuesday when the government delegation suspended its participation accusing Iran-backed rebels who control the capital of failing to keep their word.

The government demanded a written pledge from the Shiite Huthi rebels and their allies recognising an April 2015 UN Security Council resolution calling for their pullout from Sanaa and other territories they have overrun since 2014, as well as well as President Abedrabbo Mansour Hadi's legitimacy.

Hadi agreed to end the boycott after mediation by UN chief Ban Ki-moon and Qatari emir Sheikh Tamim bin Hamad Al-Thani, the UN special envoy said on Sunday.

Foreign Minister Abdulmalek al-Mikhlafi said at the face-to-face meeting Monday that the government had received a letter from the UN envoy reaffirming a commitment to "references, the talks agenda and the legitimacy" of Hadi and his government.

Mikhlafi reiterated in the speech distributed by the government delegation that the talks were the "last chance for all of us to prove that we have come for peace."

"We will excercise flexibility and make concessions for the sake of our people and for the sake of peace. We hope that the other side has the same readiness," he said.

The government has insisted that rebels should implement Resolution 2216 which calls for withdrawals, the surrender of weapons and the restoration of state institutions.

Despite a 14-month-old Saudi-led military intervention in support of Hadi's government, the rebels and their allies still control many of Yemen's most populous regions, including the central and northern highlands and Red Sea coast.

In Yemen itself, twin bombings Monday claimed by the Islamic State jihadist group hit government forces in Aden, killing at least 41 people in the latest of a spate of attacks in the southern city.