Yemen: Why is the war there getting more violent?

The civil war in Yemen, one of the Arab world's poorest countries, has grown even more violent since the start of this year.

The Saudi-led coalition backing the country's official government has spent seven years fighting a rebel group called the Houthis, using mainly air strikes They, in turn, have used drones and missiles to attack both Saudi Arabia and its ally, the United Arab Emirates.

Because of the war, Yemen is now facing one of the worst humanitarian crises in the world.

In 2011, a popular uprising in Yemen forced its long-standing authoritarian president, Ali Abdullah Saleh, to hand over power to his deputy, Abdrabbuh Mansour Hadi.

However, the new president was overwhelmed with Yemen's economic problems, and security problems such as attacks by jihadists. Furthermore, most of Yemen's armed forces felt more loyalty to the ousted president than they did to Mr Hadi.

The Houthis took advantage of his weakness.

Formally known as the Ansar Allah (Partisans of God), they champion Yemen's Zaidi Shia Muslim minority.

In early 2014, they seized control of Saada province, in the north of the country and then captured the nation's capital, Sanaa, forcing President Hadi to flee abroad in March 2015.

Yemen's neighbour Saudi Arabia was alarmed by the prospect of the Houthis taking control of Yemen, fearing it would become a satellite of its rival, Iran.

In March 2015, it and other Arab states began an air campaign aimed at ousting the Houthis and restoring Mr Hadi's government.

The coalition received logistical and intelligence support from the US, UK and France.

In August 2015, coalition ground troops landed in the port city of Aden and drove the Houthis out of the south of Yemen. However, they could not dislodge them from Sanaa or the north of the country.

The Houthis allied with the former president, Ali Abdullah Saleh, to form a "political council" to govern the area under their control. However, in December 2017, Saleh broke with the Houthis and called for his followers to fight them. Saleh was killed and the Houthis defeated his forces.

In 2018, the Saleh loyalists joined the Saudi-led coalition. Together, they launched a major offensive against the Houthis to recapture the Red Sea city of Hudaydah. Its port is the principal lifeline for millions of Yemenis at risk of famine.

After six months of fierce fighting, the two sides agreed a truce. However, the battle for Hudaydah port could resume at any point and trigger a humanitarian catastrophe.

In 2021, the Houthis launched an attack on Marib, the government's last stronghold in the north and the centre of an oil-rich province.

The UN has warned that over 100,000 people have been displaced because of the fighting there, and that two million civilians are at risk. It has called for a ceasefire.

In 2022, the air war between the Houthis and the Saudi coalition has become more brutal.

The Houthis have attacked targets in Saudi Arabia and the UAE with ballistic missiles and drones, targeting sites including oil installations but also injuring civilians.

Saudi and US officials have accused Iran of smuggling weapons such as drones to the Houthis, in violation of a UN arms embargo. Iran has denied the allegation.

The Saudi-led coalition has carried out thousands of air strikes, killing tens of thousands of people, according to the UN. These include "double tap" attacks, in which the first strike hits a group of rebels and the second one hits the people who go to their rescue.

The UN says both sides in the civil war may have committed war crimes. Both sides deny the allegation.

Yemen's official government is based in the southern port city of Aden, while President Hadi himself is based in Saudi Arabia.

The Aden government has also had to fight a separatist group called the Southern Transitional Council (STC), which wants an independent South Yemen.

In 2018, the STC's forces ousted the government from Aden and the surrounding area. Saudi Arabia intervened to reinstall the government and drew up the Riyadh Agreement of 2019. This offered the STC a role in the government in exchange for it putting its troops under the president's command.

However, the deal has not been fully implemented and tensions remain high.

The United Nations says the conflict in Yemen has produced the largest humanitarian crisis in the world, with 24.1 million people - 80% of the population - needing humanitarian aid and protection.

It predicts 19 million Yemenis will go hungry in the coming months, while more than 160,000 of them will face famine-like conditions. Reduced supplies of wheat from Ukraine, caused by the current war there, are likely to push hunger levels in Yemen even higher.

The UN estimated that by the end of 2021, the conflict in Yemen would have caused over 377,000 deaths, with 60% of them the result of hunger, lack of healthcare and unsafe water.

It says more than 10,200 children are known to have been killed or wounded as a direct result of the fighting.

Yemen has also suffered from one of the largest cholera outbreaks ever recorded, with 2.5 million suspected cases and about 4,000 related deaths since 2016.