Hezbollah commander Hussein Habib's family is still mourning his death in Syria, where he fought alongside regime soldiers. But they say they are ready to offer another son up as a "martyr".

In their town of Baalbek and other strongholds of Shiite movement Hezbollah in eastern Lebanon, it's no longer a secret that the group's members are crossing the border to bolster the ranks of government troops battling rebels.

Supporters of the movement, a long-standing ally of Syrian President Bashar al-Assad, proudly describe the fighters they say are defending Shiite land and religious sites in Syria.

Habib, a Hezbollah field commander, was killed in the countryside around Qusayr in Syria's central Homs province, according to his family.

He died about two weeks ago, they say, but they are still waiting for his body to be returned.

"We're tortured by the fact that his body hasn't been delivered and is with the gunmen (rebels)," says Fatima Habib, a cousin.

She says Habib was born in a village in the Qusayr countryside in Syria, but lived in Baalbek.

"He went to defend his family and his home," she says.

"We have lost someone dear to us and the situation is hard but if other people from the family were needed, it would be no problem for them to go and be martyred."

Habib, a married father of two, is known in the area as a senior fighter with Hezbollah, but his family insists he was killed fighting alongside the so-called Popular Committees -- groups of local pro-regime militia in Syria.

A few kilometres (miles) from Baalbek is the entrance to the town of Qasr in the Hermel region, which has been targeted by Syrian opposition shelling.

The sympathies of residents are clear: posters of Assad hang in the streets and locals refer to opposition fighters as "terrorists," just like Syrian state media.

"Terrorists were oppressing thousands of Lebanese in Syrian border villages and they asked the resistance (Hezbollah) to help defend their land and their honour," says Abu Fadi Kanaan.

As he speaks, he looks over from the roof of his house into Syria, where black smoke is rising from Qusayr in the aftermath of a regime air raid.

"We protect our homes in these villages," he says. "Yes, we send our children to defend them and we are ready to fight the battle."

The narrative advanced by Habib's family and Kanaan -- of Lebanese residents of Syria fighting to defend their homes -- is the official party line that Hezbollah chief Hassan Nasrallah first outlined last October.

He pointed to the plight of 13 villages inside Syria that are home to Lebanese citizens, saying Hezbollah members in the town "have bought weapons in order to defend themselves against armed Syrian and non-Syrian groups."

"The party has nothing to do with their decision, but I cannot tell them not to go fight," Nasrallah said.

But the claim is belied by the fact that dozens of bodies of fighters killed in Syria have been brought to Hezbollah strongholds in southern and eastern Lebanon for burial.

And senior Hezbollah leader Sheikh Nabil Qauk, speaking at a mourning ceremony for a fighter killed in Syria in April, described the group's actions in Syria as "a national and moral duty."

"Hezbollah's martyrs are the martyrs of the entire nation because they are defending their Lebanese compatriots," he said at the ceremony in south Lebanon.

One expert estimates between 800 and 1,500 Hezbollah fighters are now in Qusayr, with more further north at the Sayyeda Zeinab shrine near Damascus.

Kanaan brushes aside critics who say Hezbollah has strayed from its stated focus of "resistance" to Israel.

"We're keeping an eye on Israel... and these (rebels) are Zionists as well," he says.

"We have the right to defend Lebanese wherever they are, and particularly if they are Shiites," he adds, accusing rebel forces of trying to "finish us off."

Syria's opposition has reacted with dismay and anger to Hezbollah's role, and in recent weeks has openly targeted towns like Qasr in response.

At the entrance to the town of Hermel, some 15 kilometres from the Lebanese border with Syria, 54-year-old Ali Shamas is on the roof of a three-floor building under construction, holding pieces of shrapnel in his hands.

They come from a rocket that hit the building, which he had planned to move into with his family.

He wants the Lebanese government to protect the region.

"If you don't do your duty," he warns the government, "the resistance and the people are ready to defend themselves."