SANAA, YEMEN -- A drastic escalation in fighting between the Saudi-led military coalition and Houthi rebels in Yemen has killed and wounded hundreds of people over the past week, officials and tribal leaders said on Monday.

The U.S.-backed Arab coalition battling to restore Yemen's internationally recognized government stepped up airstrikes on rebel targets northeast of the capital, Sanaa, following a monthslong lull, while Houthis shelled government-held areas.

The sudden spike in violence across long-stalemated frontlines threatens to exacerbate the five-year conflict and complicate indirect peace talks between Saudi Arabia and the Iran-backed rebels.

The warring factions have concentrated their forces in three main areas: Nehm, a half-hour drive from the capital, Jawf, a mountainous northern district and Marib, a western province that saw one of the deadliest rebel attacks earlier this month. Fighting this week was the most intense these provinces had seen in three years, according to observers.

A wave of over 40 coalition airstrikes hit rebel targets, Houthi officials said, destroying many of their tanks and armoured vehicles.

The officials spoke on condition of anonymity in line with regulations. Tribal leaders did so for fear of reprisals.

Despite heavy losses on both sides, the Houthis are gaining ground, officials said. Rebels seized a key supply line linking Marib with Jawf, and are approaching the capital of the northwestern province. Artillery shelling in the district killed three civilians on Monday.

Throughout the day, President Abed Rabbo Mansour Hadi deliberated with military chiefs and local governors. He stressed the need to "upgrade military institutions to the highest level of training, armament and vigilance," according to a government statement. Yemeni military setbacks have drawn recent complaints that the army lacks the sort of technically advanced weaponry propelling Houthi advances.

Fighting also flared up Monday in the large government-controlled city of Taiz, where a mortar shell fired by the Houthis struck a busy market, killing three civilians and wounding ten others. Meanwhile, heavy clashes in the central province of Bayda killed 13 troops on both sides.

Yemeni Prime Minister Maeen Abdulmalik Saeed vowed government forces would "harshly confront" Houthi militias, which he accused of trying to "prolong the war and relieve the pressure and international isolation of Iran."

The Houthi offensives, he said, signal "their explicit rejection of peace efforts."

For months, back-channel negotiations in Oman between Saudi Arabia and the Houthis stirred modest hopes for reconciliation. But sharply escalating violence has put the political process on shaky ground.

Peter Salisbury, Yemen expert at the International Crisis Group, says the Houthis may be using their military successes to gain leverage before talks resume next week in Oman.

"Both sides seem to want some sort of truce," said Salisbury. "But the danger is that if the Houthis feel they're on the front foot, they'll keep pressing advances and that will make these negotiations very difficult."


Associated Press writer Isabel DeBre in Cairo contributed reporting.