Frame grab taken from footage shows smoke rising after airstrikes carried out by Russian air force near Jisr al-Shughour.

Russia is engaged in “classic asymmetric warfare” in Syria by using its military clout to prop up President Bashar al-Assad while saying it is attacking ISIS militants, Britain’s foreign minister said on Sunday.

Russia last week began striking targets in Syria – a dramatic escalation of foreign involvement in the civil war which has been criticized by the West as an attempt to prop up Assad, rather than its purported aim of attacking ISIS.

“It looks like a classic bit of Russian asymmetric warfare – you have a strong propaganda message that says you’re doing one thing while in fact you are doing something completely different and when challenged you just flatly deny it,” Philip Hammond told Reuters in an interview in Manchester.

IN OPINION: Russian airstrikes and selective outrage over Syria

He said Britain had held discussions with Russia but kept on getting the same response – that Moscow was attacking ISIS militants in Syria.

“You try talking to the Russians,” he said. “They just keep repeating their position – that is by the way also the Iranian position – and it is just incredible.”

He said that Britain needed “absolute clarity” that Assad would not be part of Syria’s future.

“That’s not some random bee in the bonnet that I’ve got; it’s that without that commitment we will never get the broad spectrum of Syrian opposition groups to sit down and agree around a table how we take forward the discussion about Syria’s future,” he said.

Hammond dismissed proposals put forward by Russia and Iran for elections, saying Syria was “a million miles away” from being able to hold a free and fair vote.

“In a country where 250,000 people have been killed and 12 million people have been displaced, half of them outside the country – how can you talk about free and fair elections?” he said.

Hammond said the key to ending the suffering caused by the four-year civil war was a managed transition to peace – even if it meant Assad retained power temporarily.

“If the price for doing that is that we have to accept that Assad will remain as titular head of state for a period of time, do I really care if that’s three days, three weeks, three months or even longer? I don’t think I do,” he said.

But Hammond said that for such a transition, Assad should make a pledge not to run in any future election and that he would give up control over Syria’s security apparatus.

He added that there was no agreement with Moscow and Tehran on such a transition.