Troops in a Saudi-led coalition arrive in Yemen’s Marib province. The alliance has boosted its presence in Yemen, apparently preparing a bid to rout Iranian-allied Houthi rebels after they killed at least 60 soldiers in a missile strike Sept. 4, 2015. (Reuters)

A Saudi-led coalition battling Shiite insurgents appears to be escalating its ground offensive in Yemen, massing troops in an oil-rich region that is within striking distance of the country’s rebel-held capital, residents and local fighters say.

Hundreds of soldiers from Saudi Arabia, the United Arab Emirates and other Arab countries have been deployed in recent weeks to participate in coalition operations in Marib province, about 75 miles east of Sanaa, the capital, according to the fighters and residents.

Thousands of Yemeni militants also are fighting on the side of the coalition against the rebels, known as Houthis, who captured Sanaa and carried out attacks across Yemen over the past year.

The coalition moves signal a possible advance on Sanaa — a heavily fortified Houthi stronghold — that could significantly raise the tempo of a war that has killed 4,500 people and caused what U.N. officials call a humanitarian disaster in the Arabian Peninsula country.

The troop buildup apparently accelerated after a Houthi missile strike in Marib last week killed 60 troops from Saudi Arabia, the UAE and Bahrain. It was the single deadliest day for the coalition, dealing a blow to ground forces that have captured most of southern Yemen from rebels since July.

If the coalition’s troop increases can apply enough pressure, the Houthis could be forced to make concessions in deadlocked peace talks in neighboring Oman, analysts say. The coalition wants to return to power the exiled Yemeni government of President Abed Rabbo Mansour Hadi.

“This big death toll from the missile strike took everybody by surprise and has placed everybody under pressure to speed up operations,” said Riad Kahwaji, an analyst and chief executive at the Dubai-based Institute for Near East and Gulf ­Military Analysis.

Coalition forces, he said, “have their sights set on Sanaa, the Houthi center of gravity, but the Houthis will put up a lethal fight.”

In March, the Saudi-led coalition launched an air war against the Houthis after they toppled the government. Saudi Arabia considers the rebels proxies for its enemy, Shiite Iran. The Houthis say they are an indigenous movement that opposes corruption and fights al-Qaeda in Yemen, a country of 25 million people.

After airstrikes did not stop Houthi advances, as many as 3,000 ground troops from the UAE led a surprise assault in July on the southern port city of Aden. The coalition forces, including Saudi-trained Yemenis, have since used an influx of Western-made tanks and other weaponry to clear most of the predominantly Sunni Muslim south of Houthi fighters.

In recent weeks, troops from the UAE, Saudi Arabia and Bahrain have deployed to Marib to link up with tribal forces that have repeatedly fought off Houthi advances. The number of foreign soldiers there has increased since last week’s deadly missile attack on the coalition soldiers, according to fighters and residents in the province.

The attack triggered an unusually heavy barrage of coalition airstrikes on Sanaa and public bursts of anger from normally low-key Persian Gulf leaders. The UAE’s Sheik Mohammed bin Zayed al-Nahyan, crown prince of Abu Dhabi, pledged after the incident to “liberate Yemen and flush out the scum.”

On Monday, the Doha-based Al Jazeera television network reported that 1,000 Qatari troops have been deployed to Marib, marking the first time that the country’s ground forces have entered the war. Qatar’s warplanes have participated in the air campaign.

Sheik Hamad Wuhait, a leader of anti-Houthi militants in Marib, said some of the Qatari forces arrived in the province Monday. It was not possible to independently verify the report.

Wuhait, who declined to give specific figures, said Yemeni fighters who were trained in Saudi Arabia and southern Yemen also are arriving in larger numbers. He said he expects Sudanese troops to be deployed soon to the area, echoing unverified claims in Arabic-language media. “We have the upper hand now, and very soon we will be purifying Sanaa from those Houthis,” he said.

Brig. Gen. Ahmed Asseri, a spokesman for the coalition, would neither confirm nor deny a coalition troop buildup but said forces will be increased “according to the mission at hand.” The coalition’s goal, he added, is to restore Yemen’s “legitimate” Hadi-led government throughout Yemen.

Analysts say Marib province is a logical staging ground for a broader coalition attack because it is near the capital and its populace is sympathetic to the mission.

The province is home to key oil production facilities and power plants that supply Sanaa’s electricity. The fighting has disabled much of that infrastructure, leading to months of crippling power blackouts in much of the country. But the oil and electrical facilities eventually could be used for development and reconstruction in areas of southern Yemen freed from Houthi control, analysts say. Parts of the south, including in Aden, were destroyed in the fighting.

“Talk of liberating Sanaa sounds a lot sexier than exploiting energy riches in Marib. But seizing that infrastructure in itself could be seen as a sort of victory,” said Adam Baron, a Yemen analyst and visiting fellow at the European Council on Foreign Relations.

Theodore Karasik, a Dubai-based expert on military issues in the Persian Gulf region, said coalition forces have made detailed preparations for an attack on the capital. Military leaders are under no illusion about the Houthis’ capabilities at guerrilla warfare, he said.

Sanaa lies in mountainous terrain that is home to tribes that are sympathetic to the Houthis, factors that would complicate such an attack, Karasik said.

Speaking by telephone from the capital, Mohammed al-Bukhaiti, a senior Houthi official, said the group’s fighters are bolstering Sanaa’s defenses.

“The coalition has been embarrassed by its losses, and if they attack us, they will pay dearly,” he said.

Naylor reported from Beirut.

Read more:

In parts of Yemen, rebels have lost control. No one else has it yet.

7 Middle East crises that are a bigger problem than Iran’s nuclear program

In Yemen’s grinding war, if the bombs don’t get you, the water shortages will

Fighting in Yemen is creating a humanitarian crisis