Yemen's warring parties welcomed a UN call for an immediate truce on Thursday as the country entered its sixth year of a conflict that has unleashed a humanitarian crisis, rendering it more vulnerable to any coronavirus outbreak.

In response, the United Nations' Yemen envoy Martin Griffiths said he would call the parties to a meeting to "put their words into action."

A Saudi-led military coalition said late on Wednesday that it backed the Yemeni government's acceptance of the UN appeal. Their foe, the Iran-aligned Houthi movement, welcomed that stance but said it wants to see implementation on the ground.

The U.S. Agency for International Development (USAID) meanwhile said it had started to reduce aid to areas controlled by the Houthis, on concerns the group hinders the delivery of assistance, a spokesperson told Reuters.

The new coronavirus has yet to be documented in the impoverished Arabian peninsula nation where conflict has killed more than 100,000 and left millions on the brink of starvation.

Following his call for a global ceasefire to focus on combating the pandemic, UN Secretary-General Antonio Guterres on Wednesday urged Yemen's parties to end hostilities and restart peace talks last held in December 2018.

The Sunni Muslim coalition, which intervened in Yemen in March 2015, supports efforts for a ceasefire, de-escalation, confidence-building measures and work to prevent a coronavirus outbreak, spokesperson Colonel Turki al-Malki said in a statement.

"The coalition's announcement... is welcome. We are waiting for it to be applied practically," a senior Houthi official, Mohammed Ali al-Houthi, wrote on Twitter late on Wednesday.

Yemen had witnessed a lull in military action after Saudi Arabia and the Houthis launched back-channel talks late last year. But there has been a recent spike in violence that threatens fragile peace deals in vital port cities.

"We have a global coronavirus pandemic threatening to overwhelm an already broken health care system," said Tamuna Sabadze, country director at the International Rescue Committee, adding that Yemen was already battling a large cholera outbreak.

Yemen has been mired in conflict since the Houthis ousted the government from power in the capital, Sana'a, in late 2014. The group still controls most major urban centers despite years of war.

Millions are dependent on humanitarian aid in Yemen, but aid agencies in recent months have increasingly complained of interference and obstruction from Houthi authorities and threatened to scale down aid if conditions did not improve.

"The Houthis have failed to demonstrate sufficient progress towards ending unacceptable interference in these operations," the USAID spokesperson said, adding that it would continue to support the most urgent life-saving assistance.

"The coronavirus crisis demonstrates now more than ever the need for our partners to be able to deliver aid to those who need it most without interference or delay."

Aid agency Oxfam warned that USAID's approach would endanger an effective coronavirus response, "leaving Yemen uniquely vulnerable to the most deadly pandemic in generations," it said in a statement.