Riyadh: A Saudi-led coalition is making slow but steady progress five days into a major offensive towards the Al Houthi militant-held capital of Yemen, a coalition source said Friday.

Giving a rare update on the fighting in Marib province, east of Sana’a, the source told AFP “things are going slowly but surely.”

Coalition-supported forces backing exiled President Abd Rabbo Mansour Hadi began their push Sunday against the Iran-backed Al Houthi militants and allied troops loyal to ousted president Ali Abdullah Saleh.

Taking Marib, in central Yemen, would allow the coalition to move on Sana’a, which Al Houthis seized last year.

“The battle will not enter its decisive phase yet,” because the coalition seeks to minimise its casualties, the source said.

The bulk of coalition troops are massed about 50 kilometres from Marib city waiting for “zero hour,” when they will move on the provincial capital, he said.

In the meantime, the coalition is targeting Al Houthi militant supply lines to Sana’a and Al Houthi stronghold of Saada in the far north.

“Progress occurred this morning north of Marib dam,” several kilometres from Marib city, where howitzers, fighter jets and helicopters targeted resistance, the source said.

“The battle to restore Marib is a vital operation because it will be the beginning of a quick end” to Al Houthis’ control, he added.

Months of coalition air strikes have failed to dislodge Al Houthis from territory they had seized in Yemen.

But the insurgents began to lose ground in July when the coalition sent in armour, troops and Yemeni fighters trained in Saudi Arabia.

Riyadh formed the Arab alliance in response to fears Al Houthis would take over all of Yemen and move it into the orbit of Iran.

An analyst has estimated the coalition has more than 5,000 troops in Yemen, supporting local forces.

The Marib offensive began after an early-September missile strike on a coalition base in the province killed 67 coalition soldiers, including 52 from the United Arab Emirates.

The United Nations says nearly 4,900 people have been killed since late March in Yemen.