US-led air strikes have failed to weaken Isis, Syria's foreign minister said, who called on Turkey to tighten control over its borders to halt the flow of fighters crossing to join the jihadist group.

Since September the US and its allies have launched more than 300 air strikes against Isis targets in Syria, but foreign minister Walid al-Moualem questioned their impact.

"All the indications say that (Islamic State) today, after two months of coalition air strikes, is not weaker," he said in an interview with the Lebanese Al Mayadeen TV broadcast on Friday, reports al Jazeera.

"If the Security Council and Washington do not force Turkey to control its borders then all of this action will not eliminate [Islamic State]," Moualem said.

Turkey, which has a 900km border with Syria, denies providing fighters with a free passage into Syria to join Isis, or supporting the jihadist group in any other way.

It has called for a no-fly zone to be established over areas of eastern Syria to establish safe areas for refugees to return to, with tens of thousands having fled into Turkey to escape the brutal three-year civil war.

However al-Moualem said that the establishment of no-fly zones would result in the partition of the country.

He said that Turkey had designs on Syrian territory.

The Syrian Observatory for Human Rights, an activist group, claimed earlier this month that 860 people, including civilians had been killed by the air strikes. However the majority killed, 746, were Islamic State militants.

US air power is believed to have played a key role in preventing Isis seize the Kurdish/Syrian border town of Kobane.

In recent weeks, the Syrian air force has stepped up the number of air strikes against rebel positions in the north and east of the country.

Targets have included Raqqa, the 'capital' of Islamic State's claimed caliphate in Syria.

Moualem said that he had recently engaged in talks with Russian President Vladimir Putin and foreign minister Sergei Lavrov aimed at re-starting peace talks with rebel groups.

It is believed that previous negotiations failed over demands from the opposition and its allies that Assad quit office.