Delegations representing Houthis and the party of ex-president Ali Abdullah Saleh have yet to head to Kuwait for the peace talks.
The UN-brokered truce went into effect on April 11.
Previous United Nations-mediated talks in June and December failed to end the war, which has killed about 6,200 people, about half of them civilians.
Fighting and airstrikes persist on several battlefronts throughout the country, especially in the contested southwestern city of Taiz and the Nehm area east of the capital Sana'a, Reuters reported.
The UN envoy to Yemen, Ismail Ould Cheikh Ahmed, urged the two parties remaining in Sana'a to commit to the talks and travel to Kuwait.
Mostly Persian Gulf Arab forces intervened in a civil war in Yemen on March 26 after the Houthis ousted the government in a revolution against corrupt officials beholden to Saudi Arabia and the West.
The United Nations has designated Yemen as one of its highest-level humanitarian crises, alongside emergencies in South Sudan, Syria and Iraq. It says more than 21 million people in Yemen need help, or about 80 percent of the population.