UN-Arab League envoy for Syria Lakhdar Brahimi has hailed a US-Russia commitment to work together to end the conflict in there.
He said it was "the first hopeful news" on Syria for a long time, but cautioned that it was "only a first step".
On Tuesday, the United States and Russia agreed to convene an international conference to find a political solution on Syria.
After talks in Moscow with President Vladimir Putin and Foreign Minister Sergei Lavrov, Secretary of State John Kerry said they would encourage both Damascus and the opposition to negotiate.
Mr Kerry and Mr Lavrov announced that they would try to organise an international conference - if possible before the end of May.
"This is the first hopeful news concerning that unhappy country in a very long time," Mr Brahimi said in a statement on Wednesday.
"The statements made in Moscow constitute a very significant first step forward. It is nevertheless only a first step."
Mr Brahimi also stressed that the US-Russian accord meant that the UN Security Council would now be able to function again.
The BBC reports the council has failed to act on Syria since the uprising against President Bashar al-Assad began in March 2011.
Russia, which supports Mr Assad, has refused to back US pressure designed to force him to step down.