Syrian elite forces and more fighters from the Lebanese Shia group Hezbollah have been sent to reinforce government troops battling rebels in the strategic border town of Qusayr, activists report.
Government fighter jets launched early on Wednesday six air raids on the rebel-held areas of the town, Hadi al-Abdallah, an activist in Qusayr, told Al Jazeera, as clashes raged between forces loyal to President Bashar al-Assad and opposition fighters on several frontlines.
"Up to 40 tanks and 40 pick-up vehicles fitted with heavy machine guns were moving towards the town from Qalamoun [in Damascus province]. Rebels will try to foil their advance," Abdallah said.
Rami Abdul Rahman, of the London-based Syrian Observatory for Human Rights network, said the latest reinforcements “indicate that the regime is gearing for a major offensive" on neighbourhoods in the north and west of the town still under rebel control.
"Despite the intense bombardment, the rebels are resisting fiercely," Abdul Rahman said.
Control of Qusayr is essential for the rebels as it is their principal transit point for weapons and fighters from across the border in Lebanon.
It is also strategic for the regime because it is located on the road linking Damascus with the Mediterranean coast, its rear base.
"If Qusayr was not strategic, the rebels would not be fighting to the death and the regime and Hezbollah would not have brought in their heavyweights," Abdul Rahman said.
Hezbollah, which is backed by Iran and is a close ally of Assad, sent almost 1,700 fighters to Qusayr more than a week ago to support the regime's assault on the rebel stronghold.
Initially Hezbollah said it wanted only to defend 13 Syrian villages along the border where Lebanese Shia Muslims live, and the Sayyeda Zeinab shrine near Damascus, which is revered by Shias around the world.
However, its fighters later encircled Qusayr as regime troops prepared for the launch of a fierce assault on the town that is home to 25,000 people.
The developments in Qusayr come as Assad's office said he was set to give an interview to Al-Manar, the television channel of Hezbollah, on Thursday.
The interview would be broadcast simultaneously on Syria's official television channels at 9pm local time (18:00 GMT), the president's office announced on its Facebook page.
Hassan Nasrallah, Hezbollah's leader, has promised that his fighters would help deliver "victory" in the battle for Qusayr, seen as a potential game-changer in Syria's drawn-out civil war in which more than 94,000 people have died, according to the UN.
For his part, Salim Idriss, head of the supreme military council of the opposition Free Syrian Army, gave warning on Tuesday that if Hezbollah fighters did not stop their aggression in Syria within 24 hours, "we will take all measures to hunt [them], even in hell".
"I will no longer be bound by any commitments I made if a decision to stop the attacks ... is not taken and implemented," Idriss, a former Syrian army brigadier-general, said.