Lebanon's army remained mute Thursday as the Syrian army and Hezbollah leader Hassan Nasrallah claimed to have captured much of the Islamic State (IS) pocket in western Syria.

If confirmed, it would be yet another setback for IS in Iraq and Syria since 2014, when it seized a cross-border swathe for its intended caliphate.

Around 40 square kilometers (miles) of the Qalamoun mountain range remained under IS control, out of the 270 square kilometers it once held in the border region, said Nasrallah, whose militia has Shiite origins.

On Lebanon-based al-Mayadeen television, a Syrian army colonel claimed the capture of Qalamoun area was nearing completion.

Hezbollah's own Al-Manar television said about 400 IS fighters were still present.

Separate Lebanese offensive

Lebanese army command said only that the fourth phase of its offensive - begun last Saturday and kept separate from the Damascus-Hezbollah effort because of Beirut's alignments with the US - should eventually lead to the eviction of all IS fighters from the border region.

Visiting troops near the border with Syria on Wednesday, Lebanese Prime Minister Saad a-Hariri said he "never doubted the Lebanese army" would defeat the IS militants inside the enclave.

On Thursday, Nasrallah said IS leaders in Qalamoun had asked for negotiations and claimed that Lebanon wanted to learn the fate of nine Lebanese soldiers taken captive in 2014 by IS when it and another militia overran the northeastern Lebanese border town of Arsal.

Iran-backed Hezbollah's role in the six-year Syrian conflict has long drawn criticism from political opponents, including Lebanese Prime Minister a-Hariri, .

US wants UNIFIL boosted

At the UN Security Council in New York on Wednesday, the US administration under President Donald Trump argued that the UN peacekeeping mission UNIFIL should be bolstered to stem arms movements by Hezbollah.

UNIFIL's mandate is due for renewal at the end of August and ambassadors for both France and Russia have said it should stay unchanged.

UNIFIL was set up in 1978 and beefed up after the 2006 border war between Hezbollah and Israel. It now has 10,500 troops monitoring the resulting ceasefire.

A Security Council vote on renewal is expected on August 30.

ipj/rc (AFP, Reuters, AP)