ADEN (Reuters) – Yemeni forces backed by armed tribesman launched an offensive to try to retake the southern provincial capital of Zinjibar on Sunday, after months of fierce fighting with Islamist militants who seized two cities and an army base in the area.

Dozens have been killed and some 54,000 civilians have fled the flashpoint southern province of Abyan, which has descended into daily bloodshed as the army faces a rising challenge from militants the government says have ties to al Qaeda.

After weeks of pleas for support from a besieged military brigade near Abyan’s capital Zinjibar, Yemen sent reinforcements aiming to flush militants out of the seaside city. Zinjibar sits down the coastline from the strategic Bab al-Mandab strait, where some 3 million barrels of oil pass daily.

“The head of the Defense Ministry sent reinforcements including tanks, rocket launchers, and 500 extra soldiers,” a local official said. “These forces began attacking (the city) backed by heavy tank shelling and rocket attacks from naval ships in order to liberate the 25th brigade just outside Zinjibar and under siege for over a month.”

The rising unrest in Abyan comes as mass protests demanding President Ali Abdullah Saleh’s ouster drag into their sixth month, paralyzing several cities and pushing the country into political limbo. Saleh is currently convalescing in Riyadh after a bomb blast on his presidential compound.

The United States and neighboring oil giant Saudi Arabia are keen to stem the chaos in the fractious Arabian Peninsula state, fearing the growing power vacuum gives room to al Qaeda’s regional wing. They were both targets of failed al Qaeda attacks launched from Yemen.

Residents told Reuters by telephone they saw army ambulances screeching through the city, filled with wounded people.

An official said some 15 militants were killed and dozens were hurt, but said only two soldiers died in the clashes.

Tribesman who joined the offensive said they sent about 450 men to Zinjibar.

Opposition groups accuse Saleh of letting his forces ease up in the south, to stoke fears in the international community that only he stands in the way of a militant takeover.