Islamic State fighters have seized villages close to the northern city of Aleppo from rival insurgents, a monitoring group said yesterday, despite an intensifying Russian air-and-sea campaign that Moscow says has targeted the militant group.

The Russian Defence Ministry said stepped-up air strikes on rebel positions in Syria killed 300 anti-Assad rebels and that it hit 60 Islamic State targets over the last day. There was no independent confirmation of the death toll.

About 200 insurgents were killed in an attack on the Liwa al-Haqq group in Raqqa province while 100 died in Aleppo, the defence ministry said.

Two Islamic State commanders were among the dead in Russia’s most intense raids since it launched strikes in Syria 10 days ago. In previous updates Russia has reported hitting 10 targets daily.

However, the Syrian Observatory for Human Rights, which monitors the fighting, said there had been no significant advances by government forces backed by allied militia in areas where ground offensives were launched this week. “It’s back and forth,” said Rami Abdulrahman, director of the Observatory.

Daesh has exploited the Russian air strikes

Iran’s elite Revolutionary Guard Corps said separately one of its generals had been killed near Aleppo, once Syria’s most populous city. Iran, like Russia an ally of President Bashar al-Assad, says it has advisers in the country.

Islamic State is now within two kilometres of government-held territory on the northern edge of Aleppo which has suffered widespread damage and disease during the four-year civil war that erupted in the wake of protests against Assad.

Syria’s military, backed by Russia, Iran and allied militias, has launched a major attack in Syria’s west to recapture land lost to non-IS rebels near the heartland of Mr al-Assad’s minority Alawite sect, an area vital to his survival.

A senior regional official close to the Syrian government said: “The Iranians are at the heart of the battle, with strength and effectiveness. Yes they are participating.”

As the operation in the west pushed ahead, Islamic State said its fighters had captured five villages in its northern offensive and killed more than 10 soldiers or militiamen.

The British-based Observatory said it was the biggest advance by Islamic State since it launched an offensive against rival rebels in Aleppo near the Turkish border in late August.

“Daesh has exploited the Russian air strikes and the preoccupation of the [rebel] Free Syrian Army in its battles in Hama, and advanced in Aleppo,” said one rebel commander with fighters in the region, using an Arabic name for IS.

Russian warplanes and warships have been bombarding targets across Syria in a campaign Moscow says is targeting IS fighters, who control large parts of eastern Syria and of Iraq.

But the campaign, which has dramatically changed the landscape of the war, appears to have mainly struck other rebel groups, some of whom had been battling to stop the Islamic State advance across Aleppo province.

US and Russian warplanes are now flying missions over the same country for the first time since World War Two risking incidents between the two air forces and their fast jets.

The United States announced yesterday that it would overhaul its failed efforts to support moderate Syrian rebels battling Islamic State, saying it would provide arms and equipment to vetted rebel leaders and their units.

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