DUBAI (Reuters) - An offensive by Yemen's Houthi group to take Marib city, the last stronghold of the internationally-recognised government, threatens to displace hundreds of thousands and complicate a renewed diplomatic push to end the war, U.N. officials say.
The gas-rich region of Marib has been a refuge for hundreds of thousands of people fleeing violence during Yemen's six-year-old war, expanding its main city rapidly.
A frontline is now roughly 30 km (18 miles) away to the city's west, a government official told Reuters, and humanitarian concerns are growing.
"An assault on the city would put two million civilians at risk, with hundreds of thousands potentially forced to flee - with unimaginable humanitarian consequences," U.N aid chief Mark Lowcock said on Tuesday, urging de-escalation.
The recent push towards Marib by Houthi forces, who control Yemen's most populous areas, comes alongside intensified drone attacks into Saudi Arabia by the Iran-aligned group. Riyadh, which leads a coalition fighting the Houthis, said one attack started a fire in a civilian aircraft at an airport in southern Saudi Arabia on Wednesday.
These escalations have coincided with a fresh push by the U.N. and the United States to end the war, which the United Nations says has created the world's largest humanitarian crisis. This push includes Washington revoking a terrorist designation of the Houthis introduced by former President Donald Trump's administration in January.
U.N. Special Envoy to Yemen Martin Griffiths has said the resumption of Houthi hostilities near Marib was extremely concerning at a time of renewed diplomatic momentum.
The United States State Department on Tuesday urged the Houthis to stop their advance on Marib and turn to negotiations.
Houthi offensives in recent days have hit camps for internally displaced persons (IDPs), causing people to flee, Yemen's information minister said.
Najeeb Al-Saadi, director of the government's IDP camp management unit, told Reuters Houthi forces on Monday hit four camps to Marib city's east. Two locations were totally evacuated, he said.
Residents in Marib city, which lies to the east of the Houthi-controlled capital Sanaa, told Reuters on Tuesday they have heard the sound of explosions this week, more strongly at night, and that planes belonging to the Saudi-led coalition are a constant sight overhead.
Yemen is divided between the internationally recognised government based in the south - supported by the Saudi-led coalition - and the Houthi movement headquartered in the north. The Houthis ousted the government from power in the capital Sanaa in late 2014.
Yemen's frontlines have largely been in stalemate for years but a major Houthi gain in Marib would leave the group in control of what historically was known as North Yemen. Marib city is also the last line of defence before Yemen's biggest gas and oil fields, which are in government hands.
The U.N.'s International Organisation for Migration (IOM)says 106,449 people have been displaced by fighting which has been bubbling along the Marib frontlines for a year.
It warned an additional 385,000 people could be displaced with a major frontline shift. There are 125 displacement sites around Marib, IOM says.
(Reporting by Lisa Barrington and Mohammed Ghobari, Editing by William Maclean)