°®Âþµº

Hizballah will join the fight against the Islamic State group on the Lebanon-Syria border, the group's chief has said, days after declaring victory against an al-Qaeda-linked Sunni militant group in the area.

Last month, a Hizballah offensive dislodged Syrian rebel Nusra Front fighters – also know as Fatah al-Sham – from the mountainous Arsal region close to the Syrian border.

Nearly 8,000 Syrian refugees and fighters from Lebanon arrived in central Syria on Thursday as part of a ceasefire deal between Hizballah and the Sunni militant group.

Hizballah chief Hassan Nasrallah said on Friday that "eliminating" IS from the mountainous area known as Jurud Arsal along the Lebanon-Syria border "is in the interests of both Lebanon and Syria".

According to Nasrallah, the Lebanese army will decide when to launch an offensive on IS, adding that "from the other side the Syrian army and Hezbollah are ready".

In the televised speech, Nasrallah said if the battle against IS is launched from both Syrian and Lebanese territory "that will lead to victory and be less costly for everyone".

"There is a final decision" to launch an offensive against IS, he said. Addressing IS directly, he added: "The Lebanese and Syrians will come at you from all sides."

He also demanded news about the fate of nine Lebanese soldiers kidnapped by IS in 2014.

There was no immediate comment from the Lebanese army, which did not take part in recent fighting in Arsal but reportedly coordinated with Hizballah. 

The powerful Shia movement is a key ally of Syrian regime president Bashar al-Assad and has been fighting alongside his forces since the onset of the war in 2011.

Around 400,000 people have been killed in Syria since the conflict began with anti-government protests, with more than half of Syria's 22 million people uprooted.

More than a million refugees fled to Lebanon adding significantly to the country's 4.5 million population.

The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes accusations and investigations.