The United Nations said on Sunday that a missile attack on a government military camp in central Yemen which killed dozens of people could derail a fragile political process that aims to calm the almost five-year-old war.

The attack on Saturday evening hit a mosque in the al-Estiqbal military training camp in Marib, a city held by the internationally-recognized government of President Abd Rabbu Mansour Hadi, as people gathered for prayer, two medical sources and forces loyal to Hadi said.

The blast was from a ballistic missile launched by Houthi fighters, the army said in a statement. It killed 79 people and wounded 81, it said.

The state news agency, carrying a report on the foreign minister, said more than 100 had been killed.

The attack "confirms without doubt that the Houthis have no desire for peace", Hadi said in a statement.

The Houthi movement has not claimed responsibility.

The United Nations envoy for Yemen, Martin Griffiths, condemned this incident and other stepped-up air strikes, missile and ground attacks around the country.

"The hard–earned progress that Yemen has made on de-escalation is very fragile. Such actions can derail this progress", Griffiths said, urging parties to direct their energies into politics and away from the battle front.

Yemen has been mired in almost five years of conflict since the Iran-aligned Houthi movement ousted Hadi's government from power in the capital Sanaa in late 2014, prompting intervention in 2015 by a Saudi-led military coalition in a bid to restore his government.

The United Nations has been trying to re-launch political negotiations to end the war and, separately, Riyadh has been holding informal talks with the Houthis since late September about de-escalation. This has seen violence decrease on a number of fronts in recent months.

On Sunday a delegation of European Union ambassadors to Yemen was in Sanaa to call for better humanitarian access and an immediate end to the conflict.

Hadi, who resides in Saudi Arabia, said the military should be on high alert after the assault.

The Yemen war has killed more than 100,000 people and pushed millions to the brink of famine.

(Cover Photo from AFP)