At least 50 rebels and pro-government troops, including a high-ranking officer, have been killed in clashes in Yemen's central province of Al-Bayda, military sources told AFP on Thursday. 

"A colonel and 19 other loyalists were killed in the past 24 hours in fighting with the Huthi insurgents in Al-Bayda district," a government military official said. 

"Thirty rebels also met their fate in battlefield clashes and air strikes."

The Huthis rarely report casualty numbers but the figures were confirmed by other military sources. 

The Iran-backed rebels have made advances in Al-Bayda province in recent weeks as they also fight for control of the strategic city of Marib in the north. 

In February, the Huthis escalated their efforts to seize Marib, the government's last toehold in the north, and the fighting has killed hundreds on both sides.

Control of the oil-rich province would strengthen the Huthis' bargaining position in peace talks.

The battle for Marib has also raised fears of a humanitarian catastrophe, as many Yemenis have fled to the area to escape fighting in other parts of the country.

The conflict in Yemen flared in 2014 when the Huthis seized the capital Sanaa, prompting Saudi-led intervention to prop up the internationally recognised government the following year.

Since then, tens of thousands have been killed and millions pushed to the brink of famine in what the United Nations calls the world's worst humanitarian crisis.  

Talks in Riyadh 

Swedish diplomat Hans Grundberg, the UN's new envoy for Yemen, arrived in Riyadh on Wednesday to meet with Yemeni and Saudi officials, marking his first trip to the kingdom since taking office earlier this month.

Also in the Saudi capital was the US special envoy for Yemen, Tim Lenderking, who met Yemeni Prime Minister Moeen Abdulmalik Saeed.

The two men discussed the latest developments, including the displacement of millions of civilians in Yemen as well as the targeting of Saudi Arabia by the Huthi rebels, the prime minister's office said on Twitter. 

As well as the bloody offensive in Marib, the Huthis have also stepped up drone and missile strikes on Saudi targets.

Two children were wounded and 14 homes damaged as Saudi forces intercepted ballistic missiles fired across the border by Yemeni rebels earlier this month.

And a few days before that, a drone hit the airport in the Saudi city of Abha, wounding eight people and damaging a civilian plane.

While the UN and Washington are pushing for an end to the war, the Huthis have demanded the re-opening of Sanaa airport, closed under a Saudi blockade since 2016, before any ceasefire or negotiations.