Russia is helping so-called Islamic State in Syria by targeting mainly moderate rebel forces in airstrikes, the UK's Foreign Secretary has claimed.
Philip Hammond said it was "unacceptable" that Moscow was "weakening the opposition" and giving an advantage to the jihadist group that it "claimed to be engaged against".
He said around 75% of Russian bombings were thought to target moderate forces who were "part of the solution to the Syrian problem".
Speaking in the House of Commons, Mr Hammond added that "with our coalition partners, including the US, we will continue to urge the Russians... to focus their fire solely on" IS.
And he also insisted no civilians have died as a result of British air strikes, according to reports received by the Government.
However, monitoring groups have questioned whether his claim includes drone strikes in Iraq.
The Government has ruled out sending British ground forces but Mr Hammond said UK non-combat troops could provide "very substantial" reinforcement to a credible ground force fighting IS in Syria and Iraq.
The foreign secretary said the Government had not dismissed the idea of providing logistics, surveillance and intelligence support for any troops that took the battle to the extremist group.
He suggested Russian leader Vladimir Putin - who has supported President Bashar al Assad - may know what the "end game" is, but efforts will go on to press the Russians to "focus their fire solely" on IS.
Meanwhile, Mr Putin's defence minister has reportedly told the Russian parliament that its air campaign in Syria will not end quickly.
He was quoted as saying "we can't expect the operation to end fast" and there was no quick end in sight because extremist groups were getting new recruits.
Unspecified other nations were failing to offer a strong contribution in the fight against terrorism, he reportedly said, adding Russia had no intention of taking part in a ground war.
Sky correspondent John Sparks has been embedded with the Russian defence ministry at the Latakia airbase in Syria.
He said: "There are a lot of Russian planes here, over 30 Russian fighters and bombers, about a dozens helicopters as well.
"Just as important is all the diggers, excavators and dump trucks here because it suggests that the Russians aren't going anywhere, anytime soon.
"They are planning to stay because they are expanding this airport, they are re-fortifying it. There is nothing temporary about this place."
He added: "There is mounting concern about civilians casualties from Russian airstrikes. People who work for NGOs have accused the Russians of not caring about collateral damage."
But a Russian official told Sky News the foreign media were making things up and the more precise they were about their targeting the more criticism they received, Sparks added.