The US hit out at the Iran-backed Houthis on Thursday for undermining the truce in Yemen and announced that President Joe Biden’s special envoy for Yemen will travel to the region.

“US Special Envoy for Yemen Tim Lenderking will travel to the United Arab Emirates, Saudi Arabia, and Oman starting [Thursday] to urge the parties to intensify UN-led negotiations in the coming three weeks, to act with urgency and flexibility, and to take the necessary steps to extend and expand the UN-mediated truce,” the State Department said.

The UN-mediated ceasefire started in April for 60 days and was renewed twice for the same period. The current truce is set to expire on October 2, and the Houthis have refused to support a six-month deal.

Lenderking’s office said a truce expansion would increase benefits to all Yemenis. “It would also pave the way for a permanent ceasefire and an inclusive, durable Yemeni-led resolution that addresses the calls of the Yemeni people for justice and accountability,” the State Department said.

But the State Department said it was concerned that recent Houthi actions were undermining the truce and threatening the lifesaving benefits it has brought to the Yemeni people. “We call on the Houthis to refrain from such actions and continue implementing the terms of the truce as they publicly committed to on August 1.”

The Houthis are continuing to detain 12 current and former US and UN staff. The US closed its mission in Yemen in 2015 after the Houthis overthrew the internationally recognized government. Last October, the Houthis detained 30 local Yemeni staff and were subsequently released with the help of Washington’s regional partners, a State Department official previously told Al Arabiya English. But the group later detained more US employees and others that worked for the United Nations.

It is unclear how many of the detainees are US employees.