Syrian army troops and Shi'ite militia fighters loyal to President Bashar al-Assad captured two southern suburbs of Damascus on Friday, killing at least 70 people, opposition activists said.

The fighters, including some from the Lebanese Shi'ite movement Hezbollah and Iraqi Shi'ites backed by Syrian army tanks, searched al-Thiabiya and Husseiniya, a Palestinian refugee camp, for pockets of resistance after overrunning them, the sources said.

The capture of the two districts, located between the two main highways leading to Jordan, strengthens Assad's hold on major supply lines and puts pressure on rebel brigades under siege for months in areas adjacent to the centre of Damascus.

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Buoyed by opposition divisions and the receding prospect of US military strikes, Assad has tried to tighten his grip on areas in the country's centre and along the coast and the north-south highways, as well as the capital and its environs - a major area of operations for his foreign Shi'ite allies.

The two suburbs are near Sayida Zainab, a district where a Shi'ite shrine is located and which Iran-backed Hezbollah and Iraqi fighters have used as a base to deploy in southern Damascus. Assad's Alawite sect is an offshoot of Shi'ite Islam.

Speaking from the south of the capital, activist Rami al-Sayyed said 20 out of the 70 people killed on the rebel side were hit by sniper fire as they tried to flee al-Thiabiya through farmland. A rebel commander said 45 Shi'ite militiamen were killed in the last 24 hours.

Sayyed said three brigades - Ahfad al-Rasoul and al-Umma and Aknaf al-Bayt al-Maqdesi, which is mainly comprised of Palestinian refugees - had repeatedly asked for back-up from better equipped rebels brigades in eastern Damascus.

“They were let down. The loss of these districts is largely due to lack of coordination and the reluctance to assist the defenders,” Sayyed said.

Al-Thiabiya and Husseiniya have been hit by multiple rocket launchers for the past week from an army camp situated on the high ground near the area, providing cover for Shi'ite fighters who did most of the street fighting, opposition sources said.

In a last-ditch effort to save the two districts, rebels attacked loyalist forces in Sayida Zainab with mortar bombs and automatic weapons on Thursday, but the counter-offensive failed.

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The Iraqi and Lebanese militia backed by Syrian army tanks and fighter jets overran Sheikh Omar, another southern suburb near Sayida Zainab, earlier this week, putting pressure on several Islamist rebel brigades trying to hold onto strategic outskirts of the capital.

The 2-1/2-year war has killed more than 100,000 people and forced millions from their homes into sprawling refugee camps in neighbouring countries.

It began with peaceful demonstrations against four decades of Assad family rule. With Shi'ite Iran and Sunni heavyweight Saudi Arabia backing opposing sides in the conflict and Russia blocking Western efforts to push Assad aside, there is little sign of an end to the bloodshed.

Regional security officials say fighters from Iraq, Iran, Yemen and Hezbollah are in Syria supporting Assad, as well as foreign fighters and Syrian expatriates on the rebel side.

The total number of foreign fighters on both sides runs in the tens of thousands, they say.

Reuters