The Yemen war is entering a new and potentially decisive phase as Gulf nations build up ground forces to battle rebels in the country's north and rebel-held capital, analysts say.

After five months of air strikes by a Saudi-led coalition and ground combat between Iran-backed rebels and coalition-supported fighters, Yemen "is bracing for a new and more deadly phase of violence in the north", said April Longley Alley of the International Crisis Group.

"Both sides are gearing up for a major conflict in the north and especially in Sanaa."

Overnight and yesterday, coalition warplanes pounded rebel positions in Sanaa amid the build-up.

The Shiite Huthi rebels, who have long complained of marginalisation, swept down from their northern mountainous stronghold last year to seize Sanaa unopposed.

They advanced on second city

Aden in March, forcing President Abedrabbo Mansour Hadi to flee to Saudi Arabia.

Riyadh then organised an Arab coalition aimed at restoring Hadi's internationally backed government.

Months of air strikes failed to dislodge the Huthis, however.

Then, in July, the rebels were hit by major setbacks after the coalition, according to military sources, sent in armour, troops and Yemeni fighters trained in Saudi Arabia.

Anti-rebel forces have since retaken Aden and four other southern provinces.

The coalition appears determined to recover yet more territory, especially since Friday's killing of dozens of coalition troops in a Tochka missile strike on their Safer base in Marib province east of Sanaa, Alley said.

The death of 45 soldiers from the United Arab Emirates, 10 from Saudi Arabia and five from Bahrain was by far the greatest loss suffered by the coalition - and highlighted

the extent of its involvement on the ground.

Marib has become a strategic location for reinforcements from Saudi Arabia, Qatar and the Gulf, according to media reports and Yemeni military sources.

The missile attack shocked the Gulf states, but the coalition vowed to press on.

Riyadh formed the Arab alliance in response to fears that the Huthis would take over all of Yemen and move it into the orbit of Sunni Saudi Arabia's Shiite regional rival Iran.

The Tochka attack was "a turning point”, said Andreas Krieg, a consultant to the Qatari armed forces and a lecturer at King's College in London.

He said the coalition “will prepare a greater deployment of ground troops" to support local forces trained and equipped over the past six months.

"There will be a push from the north and the south towards Sanaa.”