The top United Nations human rights forum is expected to condemn Syria for crimes against humanity at an emergency session on Friday, European and Arab diplomats said.
The move is also designed to put pressure on China and Russia to take a stronger stand against the government of President Bashar al-Assad, they said.
More than 20 member states back the U.N. Human Rights Council holding a special session, which is to be announced on Wednesday, they added.
The 47-member forum's third session on Syria in eight months is being convened days after a U.N. commission of inquiry said Syrian security forces had committed murder, torture and rape during their crackdown on pro-democracy protests.
This is very much being led by the Arab group. Some Arab ambassadors are at least as concerned as the European Union and United States and possibly more, Britain's ambassador Peter Gooderham told Reuters.
There is no question that the resolution will be very hard-hitting at the Council's session on Friday, he said. It is all intended to build up the maximum pressure that the Human Rights Council can apply.
An Arab diplomat in Geneva, who declined to be identified, told Reuters: Arab support is there, the three Gulf Cooperation Council countries who are Council members -- Qatar, Kuwait and Saudi Arabia -- and Jordan. I'm sure Libya will be with us too.
It is meant to be a tool for later action in New York, he said, referring to the General Assembly and Security Council.
On Sunday, the Arab League imposed sanctions on Damascus over its crackdown, in which more than 3,500 people have been killed since March, including 256 children, according to the United Nations. The EU weighed in one day later, further tightening the financial screws on Damascus.
Turkish Foreign Minister Ahmet Davutoglu said on Tuesday Turkey would announce its sanctions soon.
An EU draft resolution to be presented to the U.N. rights forum for adoption, obtained by Reuters, strongly condemns continued widespread, systematic and gross violations of human rights and fundamental freedoms by the Syrian authorities.
These included executions, killing and persecution of protesters, activists and journalists, as well as arbitrary detentions, enforced disappearances and torture.
The resolution will certainly be adopted, no question, it has wide support, the Arab diplomat said.
The draft text recommends that the General Assembly consider the commission of inquiry's report and refer the report to the Security Council for its consideration and appropriate action.
The Security Council has the power to refer a country to the prosecutor of the International Criminal Court (ICC).
This is probably the most controversial element in the resolution, Gooderham said.
Russia and China, which both have oil concessions in Syria, teamed up last month to veto a Western-backed Security Council resolution condemning Assad's government for violence.
The British envoy, asked about chances of winning support from China and Russia for the resolution, said: Naturally we hope they will support this and not call a vote on the resolution as they did in August where they found themselves in a very small minority of only four states, he said.
We hope that they will look at the merits. The seriousness of the evidence is incontrovertible, he said.
The U.N. commission of inquiry, which interviewed 223 victims and witnesses including defectors from the Syrian army, catalogued executions, torture, brutal rapes and abductions.
They didn't even have access to Syria. Imagine what is happening really inside the country, the Arab diplomat said.
It is close to the Iraq of Saddam Hussein, it is not any different in terms of human rights, he said.
(Reporting by Stephanie Nebehay; editing by Andrew Roche)