The United Nations is "unable to independently corroborate" that missiles and drones used in attacks on Saudi oil facilities in September "are of Iranian origin," Secretary-General Antonio Guterres told the Security Council on Tuesday.

Sudan's prime minister said on Sunday Khartoum had reduced the number of troops it has in Yemen from a peak of 15,000 to 5,000, confirming a drawdown in a conflict which he said could not be solved militarily.

A group of Houthi prisoners released by Saudi Arabia arrived in the Yemeni capital Sanaa on Thursday, Reuters witnesses said, in a step that may encourage efforts to end a nearly five-year war in the country.

The Saudi-led coalition fighting Yemen's Huthi rebels said Tuesday it will release 200 insurgents, as efforts pick up pace to end the conflict in the impoverished country.

Saudi Arabia is intensifying informal talks with the Iran-aligned Houthi movement on a ceasefire in Yemen, sources familiar with the discussions said.

Yemen’s Houthi movement said on Friday its air defenses downed a U.S.-made ScanEagle drone near the Saudi border, the group’s military spokesman said.

The United Arab Emirates said on Wednesday that its troops have left Yemen's southern port of Aden and returned home, handing over control to Saudi Arabia which is leading an Arab military coalition engaged in Yemen.

Yemen's government and Huthi rebels have set up joint observation posts as part of de-escalation moves in the flashpoint city of Hodeida, a move the United Nations welcomed on Wednesday.

The Houthi group in control of Yemen's capital released hundreds of prisoners on Monday in a unilateral move, which the United Nations hoped would help revive a stalled peace process after months of failed efforts to push through a prisoner swap.

Air strikes blamed on the Saudi-led coalition killed at least 16 people in Yemen's disputed province of al-Dhalea on Tuesday, two residents and the Houthi-run al-Masirah TV said.

The Saudi-led coalition launched a military operation north of Yemen's port city of Hodeidah against what it described as "legitimate military targets", State-run Ekhbariya TV reported on Friday.

Yemen's Houthi group said on Wednesday it had identified dozens of sites in the United Arab Emirates as possible targets, in an attempt to underscore its military clout following a weekend attack it claims to have carried out on Saudi oil facilities.

At a weapons exhibition in July in Yemen's Houthi-controlled capital Sanaa, military officials whipped silken sheets off what they said were newly-developed drones and missiles.

The U.S. State Department called on American citizens to "exercise increased caution" while travelling to Saudi Arabia, a travel advisory posted on its website said on Wednesday.

Yemeni government officials have begun indirect talks with United Arab Emirates-backed southern separatists in the Saudi Red Sea city of Jeddah to end fighting in Aden and other southern provinces, a Yemeni official said on Wednesday.

Saudi Arabia has deployed more troops in southern Yemen to try to contain clashes between nominal allies in the Saudi-led military coalition fighting the Houthis that risk further fragmenting the country.

Saudi Arabia is struggling to hold together a military coalition fighting Iran-aligned Houthis in Yemen after local allies turned on each other in a power struggle that has strained Riyadh's alliance with its main regional partner, the United Arab Emirates.

Yemen's Houthi movement's air defenses on Wednesday downed a United States drone MQ-9 in Dhamar governorate, southeast of the Houthi-controlled capital Sanaa, the group's Al-Masirah TV quoted the group's military spokesman as saying.

The president of Yemen's Southern Transitional Council (STC) headed with a delegation to the Saudi city of Jeddah on Tuesday after accepting the kingdom's invitation to a summit on the crisis in the Yemeni port city of Aden, the council said.

Yemen's Houthis launched more drone attacks on Saudi Arabia's Abha international airport on Friday, halting air traffic there, the Iran-aligned group's military spokesman said.