DUBAI: Tens of thousands of people have been displaced by fierce fighting in Yemen's Marib province this year, the UN's migration agency said Thursday, with figures surging as clashes intensified last month.

The battle for Marib city, the internationally-backed government's last northern stronghold, could change the course of a civil war that has forced millions of people to flee their homes over the course of its seven years.

"From January 1 to September 30, IOM recorded more than 55,000 people displaced in Marib governorate in the areas where our displacement tracking and rapid response teams have access," the International Organization for Migration told AFP.

The Iran-backed Huthi rebels began a big push to seize Marib in February and, after a lull, they renewed their campaign in September, prompting intense air bombardments from Saudi-led coalition forces backing the government.

Nearly 10,000 people were displaced last month alone -- the highest numbers in the province this year, the IOM said.

Coalition strikes intensified this week, when the alliance reported four successive days of operations south of Marib and around 550 rebels killed, a toll that could not be independently verified.

At least 50 dead as fighting intensifies for Yemen's Marib

Marib had between 20,000 and 30,000 inhabitants before the war.

But its population ballooned to hundreds of thousands, as Yemenis fled frontline cities for its "relative stability" and the chance to maintain a livelihood, Ahmed Nagi of the Malcolm H Kerr Carnegie Middle East Center, has told AFP.

But with about 139 refugee camps in the province, according to the government, hosting approximately 2.2 million people, the displaced civilians have become caught in the line of fire once again.

"Critical infrastructure such as bridges and roads have also been damaged and destroyed," the United Nations Office for the Coordination of Humanitarian Affairs said in a statement on Wednesday.

The UN has called Yemen's war the world's worst humanitarian catastrophe.

The rebels overran the capital Sanaa, just 120 kilometres (75 miles) west of Marib, in 2014, prompting the Saudi-led intervention to prop up the government the following year.

Tens of thousands of people have been killed.