Russia "must turn words into actions" to influence the situation in Syria started by the cessation of hostilities in the country, the UK's ambassador to the United Nations has said.
Matthew Rycroft welcomed the UN's adoption of the Security Council resolution on the ceasefire in Syria, which started on Friday, but said much more needed to be done.
He called for "transparent monitoring" of the truce, the release of "arbitrarily detained people" and an end to the "unacceptable" obstruction of medical supplies to besieged and hard-to-reach areas.
"If implemented fully, this agreement could be the most significant step forward in the past five years; a step that brings us closer to an end to the violence; a step that brings the conclusion of this conflict into sight, and with it, hope for a political transition," he said.
Negotiations on transition in the country will reconvene in Geneva on March 7 and Mr Rycroft urged Russia to use its influence to positive effect.
He said: "Russia must turn words into actions and use its unique influence on the Assad regime, its affiliated militias and other backers to abide by this agreement.
"If they do, some much-needed confidence will be brought to our hopes for a political settlement. If they don't, we will falter again and the spiral of violence will continue.
"We should not forget that 1,380 civilians have been killed and 5,789 injured by Russian and regime air strikes since Russia began its campaign in Syria, including attacks on at least three IDP and refugee camps."
The cessation of hostilities was an "overdue milestone", he said, adding: "But rather than dwell on our past failures, let us now seize the momentum and see urgent progress towards a political transition away from Assad towards a government that represents all Syrians."
Using another name for the Islamic State extremist group, Mr Rycroft said: "This is the only way to end the longer-term conflict and in doing so, allow us to defeat the Daesh threat."