Oct 16 - The city of Taiz is rapidly emerging as the most important battlefront in Yemen's reignited civil war, pitting the Iran-allied Houthis against the internationally recognised government, which is backed by a Saudi-led coalition.

Houthi forces have encircled Taiz in recent weeks by cutting its main road south to Aden, causing widespread displacement and worsening a humanitarian crisis. Here's what you need to know: WHY IS TAIZ SO IMPORTANT?

Any Houthi victory in Taiz, Yemen's third-largest city, would mark one of the biggest turning points in the country's long civil war, which resumed this summer after a four-year truce.

Taiz city has an estimated population of almost 600,000, said Katja Juric, Aden-based head of programmes for the International Organization for Migration (IOM). Government sources said 80,000 had fled in the latest fighting.

Taiz has been on the frontline between the Houthis and the government since the first days of the conflict that started in early 2015 and has long been seen as a bastion of opposition to the Iran-allied group.

It is the last major urban stronghold of anti-Houthi forces in the southern highland area of Yemen: the rugged hills above both Aden, where the internationally recognised government is based, and the flat coastal plain around the Bab el-Mandeb Strait.

A Houthi takeover of Taiz would make it much harder for government forces to maintain their counterattack around Bab el-Mandeb and keep the Houthis at arm's length from Aden.

It would also mean a resounding symbolic defeat for the government and the military coalition of Saudi-backed Yemeni forces fighting the Houthis. WHAT'S THE MILITARY SITUATION AROUND TAIZ?

For years the city has sat at the tip of a government salient stretching north into Houthi territory.

The Houthis held areas to the north, east and west of Taiz, while government forces had the city and its immediate surroundings including Jebel Sabar, the high mountain rising above it to the south.

As fighting in Yemen resumed in recent weeks, the Houthis began making advances to cut off Taiz by seizing territory to the south of Jebel Sabar along the road to Aden, which snakes about 200 km (125 miles) through rugged hills where fighting is slow and difficult.

Sections of the road are now under Houthi control, including at the towns of al-Turbah and Mudiriyat al-Misrakh, leaving Taiz encircled since early October, with the Houthis sometimes shelling government positions in and around the city.

Government forces, backed by airstrikes from the Saudi-led coalition, are trying to drive the Houthis back from their recent gains and reopen the road, but were still losing ground around Taiz rather than recapturing territory in mid-October. WHY IS TAIZ A STRONGHOLD OF OPPOSITION TO THE HOUTHIS?

Taiz had a long history of difficult ties with rulers from north Yemen and was a hotbed of the 2011 Arab Spring uprisings that toppled veteran former president Ali Abdullah Saleh.

While the Houthis adhere to the Zaydi school of Shi'ite Islam, Taiz is predominantly Sunni Muslim.

Saleh and the Houthis joined forces to seize the capital, Sanaa, in 2014, derailing a political transition that arose out of the Arab Spring and had led to a proposal for a federal, democratic state.

In early 2015, army units loyal to Saleh seized positions in the city, leading to big protests there followed by armed clashes. Protesters accused Saleh and the Houthis of mounting a coup d'etat.

Months of fierce fighting in and around the city followed, with the Houthis and Saleh's army units battling local fighters and army brigades from Yemen's now fragmented military that backed the government.

Taiz citizens endured shelling, sniper fire and terrible shortages in a long siege before government forces eventually drove the Houthis and their allies from the city and re-established a land route to Aden.

The fighting in the city lasted throughout 2015 and parts of 2016, and the siege ran for long stretches until 2017. WHAT IS THE HUMANITARIAN SITUATION IN TAIZ?

The latest fighting has displaced at least 121,000 in Taiz province, according to the IOM, though many of these are from rural areas outside the city.

Inside Taiz, residents have told Reuters about the shortages they now face of basic items and the huge increase in prices they see in the city markets since the Houthis cut the road to Aden.

Aid agencies have reported widespread shortages of fuel, food, medicines and clean water. Wheat flour stocks in the city are nearly exhausted, the World Food Programme said in mid-October.

The situation risks worsening existing health problems. The UN children's agency UNICEF recently found that one in three of the children it screened in Yemen was malnourished. Cholera, dengue and malaria are all present in Yemen too. WHAT HAPPENS NEXT?

Government forces backed by Saudi airstrikes are still trying to take back territory to reopen the road, but there is no guarantee they will succeed.

The Houthis, who have upped their attacks on Saudi targets while showing themselves better armed and organised than in earlier phases of the war, are meanwhile trying to cement their siege of Taiz and move closer towards the city. That might lead to a prolonged siege of the kind that Taiz experienced in the earlier phase of the war.

It's also possible the Houthis might try to take the city. Local opposition means resistance could be fierce and any such attempt could cause a long, bloody battle.