By Kylie MacLellan and William James
LONDON (Reuters) - British Foreign Secretary Philip Hammond said on Wednesday that Russia's continued focus on targeting most of its air strikes in Syria against opposition forces rather than Islamic State was helping the militants advance.
Russia, one of Syrian President Bashar al-Assad's staunchest allies, is carrying out a campaign of air strikes it says are aimed at Islamic State (IS) militants, but which also support Assad's forces.
"The majority of Russian air strikes continue to target Syrian opposition forces rather than Daesh," Hammond told parliament, using the Arabic term for Islamic State.
"With our coalition partners including the United States, we will continue to urge the Russians at every opportunity to focus their fire solely on Daesh. It is unacceptable that Russian action is weakening the opposition and thus giving advantage to the very Daesh forces that they claim to be engaged against."
At last month's G20 summit in Turkey, Russian President Vladimir Putin told British Prime Minister David Cameron he was seeking to do more to focus Russian efforts on combating Islamic State, a source in Cameron's office said.
Hammond said that while Russia had increased the number of strikes against IS since the Russian plane crash in Sinai in October for which the group claimed responsibility, it was still only targeting around a quarter of its strikes on the militants.
"What the Russians have done so far is at best ambiguous," Hammond said.
"It is still only around 25 percent of the total of their air strikes, the remainder are targeted against the moderate opposition and that is deeply unhelpful to put it mildly."
Hammond also said a U.S. target to reach agreement on a national Syrian ceasefire at talks of world powers in New York on Friday would be "highly challenging".
(Editing by Stephen Addison)