The US envoy seeking to end Yemen's brutal war headed back to the region Monday as Houthis press ahead with an offensive to take the government's last northern toehold.

Tim Lenderking, named by President Joe Biden in his first days in office in a sign of renewed US effort to address the humanitarian catastrophe, will visit several Gulf nations on a trip that will last through March 3, the State Department said.

His discussions "will focus on the United States' dual-track approach to end the conflict in Yemen: a lasting political solution and humanitarian relief for the Yemeni people," a statement from the State Department said, without specifying his exact stops.

Lenderking was in the region less than two weeks ago when he held talks in Saudi Arabia, a US ally to which Biden has pledged to cut off support for offensive operations in Yemen amid outrage over civilian casualties.

On his return to Washington, Lenderking said the administration was working "to energize international diplomatic efforts with our Gulf partners, the United Nations and others to create the right conditions for a ceasefire and to push the parties toward a negotiated settlement to end the war in Yemen."

The diplomacy comes as the Houthis shrug off international calls for restraint and seek to capture Marib, the fledgling Saudi-backed government's last major bastion in the north which lies next to some of Yemen's richest oil fields.

The Biden administration in one of its first moves ended a last-minute designation by former president Donald Trump's team of the Iranian-linked Houthis as a terrorist organization.

The move came after humanitarian groups warned that the designation would severely hinder operations in a country where 80 percent of people survive thanks to aid.

-AFP