Fighting between Yemen’s government forces and the country’s Houthi rebels in the central province of Marib killed at least 140 fighters this week, tribal leaders and security officials said Thursday.

The most intense clashes have been underway over the past 24 hours in the southern parts of the largely-government controlled province, in the districts of Abdiya and al-Jubah, they said.

The Iran-backed Shiite Houthis have stepped up their push in the strategic province over the past weeks while also escalating cross-border attacks on Saudi Arabia, which is leading a military coalition that has been fighting on the government side against the Houthis.

The escalation comes as government forces launched a counteroffensive to wrestle areas that had been overrun by the rebels last week, the officials said, speaking on condition of anonymity because they were not authorized to speak to the media. Tribal leaders asked not to be named for fear of reprisals.

Yemen has been convulsed by civil war since 2014 when the Houthis captured the capital, Sanaa, and much of the north of the country, forcing the internationally recognized government to flee to the south, then to Saudi Arabia.

The Saudi-led coalition entered the war in March 2015, backed by the United States, to try restore the government to power. Despite a relentless air campaign and ground fighting, the war has deteriorated largely into a stalemate and spawned the world’s worst humanitarian crisis.

The Houthis have for years attempted to take oil-rich Marib to complete their control over the northern half of Yemen. In recent months, they accelerated their push. The fighting has claimed a high number of fighters from both sides in Marib in the past several weeks.

Associated Press