Tim Lenderking will travel to the United Arab Emirates, Oman and Saudi Arabia starting August 11, while members of his team travel to Jordan, hoping to secure an expansion of the UN-mediated truce between Yemen's warring parties.

The efforts aim to "pave the way for a permanent ceasefire and an inclusive, durable Yemeni-led resolution to the conflict," the department said in a statement.

The United Nations announced on August 2 that a four-month truce had been extended until October 2, buying time for negotiations to establish a longer, more durable ceasefire.

Yemen has been gripped by conflict since the Iran-backed Huthi rebels took control of the capital Sanaa in 2014, triggering a Saudi-led military intervention in support of the beleaguered government the following year.

The State Department said Lenderking will also discuss recent instability in the central province of Shabwa, and urge other governments to step up financial assistance for Yemenis.

"We urge donors both to give generously and to make previous pledges immediately available for the sake of the people of Yemen," the department said.