Britain has launched a renewed attack on Russia's support for Syrian President Bashar Assad, accusing the Kremlin of giving him a "green flag" to commit human rights atrocities against his own people.
Speaking at an international donors conference in Brussels, International Development Secretary Penny Mordaunt defended US-led missile strikes against the Syrian regime, saying Moscow had blocked every attempt to hold it to account for its illegal use of chemical weapons.
Her intervention came as Russia announced it would be providing Syria with a sophisticated new air defence system after the strikes earlier this month.
Colonel General Sergei Rudskoi said the new missile defence systems would be delivered "soon".
He did not specify the type of weapons, but Russian media reports have said Moscow was considering supplying Damascus with the S-300 surface-to-air missile system.
Ms Mordaunt said Britain had joined the "limited and targeted" missile strikes as the regime had shown it had "the capability and the intent" to use chemical weapons against the civilian population.
"It is also clear the Syrian regime and its backers, Russia and Iran, will attempt to block every diplomatic effort to hold the regime accountable for these reprehensible and illegal tactics," she said.
"In wielding its UN veto 12 times on Syria, Russia has given a green flag to Assad to perpetrate human rights atrocities against his own people."
The United Nations is seeking to raise more than 7 billion dollars (£5 billion) at the donors conference attended by around 80 countries, organisations and partners backing Syria.
Britain has said it will donate another £250 million over the next two years, taking its total support to £450 million this year, with another £300 million in 2019.
The European Union hopes the meeting will provide fresh impetus to stalled peace moves under the UN.
EU foreign policy chief Federica Mogherini called on Russia and Iran to exert pressure on the regime to rejoin talks.
"The opposition with whom we have been working in these years is today more united and ready to sit for negotiations," she said.
"We believe that the only sustainable peace for Syria will be linked to a political process under UN auspices."