European Union foreign ministers say they will not renew an arms embargo on the Syrian opposition, due to expire on Saturday.
But there was no immediate decision to send arms to Syrian rebels and all other sanctions remained in force, after lengthy talks among divided ministers in Brussels, reported the BBC.
Russia said it would "directly harm" the prospects of an international peace conference on Syria.
Deputy Foreign Minister Sergei Ryabkov says Moscow, which together with Washington, has been trying to organise the conference for next month, is disappointed with the EU move, the Itar-Tass news agency reported.
A spokesperson for Syria's National Coalition, Louay Safi, was quoted by the news agency AFP as saying that the EU move was "a positive step" but that the coalition was "afraid it could be too little, too late".
The BBC's Middle East correspondent says while the lifting of the EU arms embargo is theoretically good news for the fractious Syrian opposition, it is clearly going to be some time before it has any effect on the battlefield.
Its authors, especially Britain, hope the decision itself will send a strong enough signal to President Bashar al-Assad that it is time to hand over power.
However, the BBC says that is extremely unlikely particularly as government forces have recently been making significant gains.
