Assad vows to fight on

President Bashar al-Assad vowed on Tuesday to fight on in what he called Syria's war against terrorism, showing no sign of compromise in his first major address since peace talks broke down in April.

Assad said he would win back "every inch" of Syria and said Aleppo would be a graveyard for the hopes and dreams of Turkish President Tayyip Erdogan, a major sponsor of the insurgents battling to topple him.

"Our war against terrorism is continuing," Assad said in a speech to parliament broadcast by state TV. "As we liberated Tadmur (Palmyra) and before it many areas, we will liberate every inch of Syria from their hands. Our only option is victory, otherwise Syria will not continue."

The Syrian army and allied militia, aided by Russian air strikes, recovered control of Palmyra from Islamic State insurgents in March. In addition to the war with Islamic State, Assad is fighting rebels who include groups that have received support from his foreign enemies, Turkey included.

Aleppo, Syria's largest city and pre-war commercial hub, and the surrounding area at the border with Turkey have comprised a major theatre in the war, divided between areas of government and rebel control. Escalating fighting there helped ruin the cessation of hostilities agreement agreed in February.

Assad accused Erdogan of recently sending thousands of militants to Aleppo. Russia, which has been bombing in support of Assad since September, said on Saturday more that 2,000 militants had mobilised in the Aleppo area.

Russia said on Monday its air forces would provide "the most active" support to Syrian government troops so as not to let Aleppo and the surrounding area fall into the hands of fighters it called terrorists.

Meanwhile, thousands of civilians yesterday fled along the Islamic State group's supply lifeline in northern Syria as US-backed fighters closed in from three sides.

The offensive is one of two major assaults on the jihadist supply line from the Syrian-Turkish border to IS's bastion of Raqa.

The Syrian Democratic Forces alliance began its offensive against Manbij just over a week ago, crossing the Euphrates River and pushing west towards the town.

"We have surrounded Manbij from three sides and operations are progressing well," said Sherfan Darwish, who is leading the SDF offensive.

"Daesh has begun allowing civilians to flee towards the west, whereas before they had banned anyone from leaving," Observatory chief Rami Abdel Rahman said, using an Arabic acronym for IS.