Yemen is at the centre of a proxy war between Iran and Saudi Arabia
The Yemeni capital Sanaa is being pounded by air strikes as conflict enters its eighth year.
Yemen’s Marib province is being bombarded by pro-government forces and Shi’ite rebels.
The province is important because it holds Yemen’s main energy hub Marib on the Gulf of Aden and goes through it into the Arabian Sea.
It is also home to a strategic power plant that supplies the oil-rich south of the country.
There has been fighting in the province since April when, according to the Saudi-led coalition backing the Yemeni government, the Houthis entered it and occupied the power plant.
They also laid siege to Marib city, which lies in the district of al-Ain, and an ammunition dump.
The Houthis are led by the group, Ansar Allah, which means Supporters of God.
In 2014, they drove out the previous president, Abd-Rabbu Mansour Hadi, who fled to Riyadh.
The government, in power in Sanaa, is backed by a Saudi-led coalition.
Yemen’s crisis has deepened in recent months with aid groups warning of worsening food shortages and an outbreak of cholera.