Troops loyal to embattled Syrian President Bashar Assad have made strategic gains against rebel forces in recent days.

This is possibly to strengthen the regime's position if Western and Russian diplomacy can set up talks aimed at ending the civil war now in its third year.

However, the Damascus regime doesn't appear to have scored any decisive victories in the heavy fighting, although it's made significant advances in southern Syria that could block a rebel push aimed at the capital from that region.

The rebels have been pushing toward Damascus from the north for many months without a major breakthrough but the regime's growing control of the south looked like it could be a game-changer.

The regime's successes threaten a vital major rebel-held corridor from neighboring Jordan for arms and a growing flow of fighters trained in the Hashemite kingdom by U.S. and British Special Forces.

The key regime advance was taking the town of Khirbet Ghazaleh on the highway linking Jordan and Damascus Sunday. That gave them control of a large area of Deraa province, where the war began in March 2011 with an uprising against the Assad family's brutal 40-year rule.

But important though the regime's southern gains may be, the decisive fighting appears to be further west and north.

That's where regime forces and their allies, including Hezbollah from Lebanon, have been battling to establish control of territory running south from the heartland of Assad's minority Alawite sect on the Mediterranean coast to the strategic city of Homs, linked to Damascus, and land east of the Lebanese border.

This territory, anchored on the Alawites' traditional turf, is seen as a final redoubt for Assad and his followers if Damascus falls.

They would control two major ports, Tartus and Latakia, several military airfields and the mountains to the east, thus maintaining a lifeline from the regime's allies, Russia and Iran.

At the same time, this terrain would abut territory in northeastern Lebanon centered on the Bekaa Valley, Hezbollah's strategic heartland. That would allow Iran to go on funneling weapons, such as the long-range and air-defense missiles the Israelis keep attacking, to Hezbollah with which to threaten Israel even if Damascus, the Syrian end of an air bridge from Iran, was no longer in Assad's hands.

The regime, or rather its allies like Hezbollah and more recently pro-Syrian Palestinians, has been battling hard to secure the Qusair region of Syria east of the Bekaa and the Hezbollah-held Hermel sector.

This is a corridor that both sides have used for men and weapons since the war began. If the regime can't hold it all, the link with Hezbollah could be broken.

Assad is reported to have said in April that the fighting around Qusair is the "main battle" for his forces.

The town of Qusair, taken by the rebels a year ago and currently the scene of heavy fighting in which Hezbollah has taken considerable losses, is besieged by regime forces on three sides.

On Friday, the Syrians said they dropped leaflets calling on the rebel garrison to surrender. As far as is known, the rebels are still there.

U.N. High Commissioner for Human Rights, Navi Pillay, said she fears atrocities of the region is overrun. She said the Syrian buildup in the area appears to be "in preparation for a large-scale attack to uproot the armed opposition" that could result in the slaughter of civilians.

Israeli reports said the bulk of the regime's infantry forces engaged in the Qusair fighting, and increasingly in other war zones, is a new 150,000-strong militia trained by Iran's elite Al-Quds Force.

The new force, known as Jaish al-Shabi, or Popular Army, reportedly comprises Hezbollah fighters, Iranians and Shiites from Iraq and the Persian Gulf states who are taking over from the hard-pressed Syrian army.

Most of the military conscripts are Sunni, the majority sect leading the war against Assad, and they're thus deemed unreliable by the regime as the war drags on.

The Israeli claim cannot be substantiated but it suggests an Iranian involvement on the ground in Syria far greater than hitherto known.

That lends some weight to speculation that Iran's determined to hold onto Syria, its strategic foothold in the Levant, even if Tehran has to take over the war itself.