The United Nations General Assembly has voted 137 to 12 to approve a non-binding resolution calling for an immediate halt to the Syrian government's crackdown on the uprising against President Bashar al-Assad's rule.
The vote on Thursday followed another day of violence as opposition activists said at least 22 people had been killed in a continuing military assault on opposition strongholds.
A prominent blogger and other leading activists were also arrested on Thursday, just hours before the UN vote on the crisis.
China, Russia and Iran were among the nations that opposed the resolution that condemned "widespread and systematic violations of human rights in Syria" and called for the Syrian president to abide by an Arab League plan for him to relinquish power.
The resolution was proposed by Arab states including Qatar, Egypt and Saudi Arabia, as well as Western powers which have expressed support for protesters in Syria, including the US, the UK and France.
Seventeen other members of the 193-nation body abstained from voting.
Vitaly Churkin, the Russian ambassador to the UN, said his country had voted against the resolution because it felt it was one-sided and did not apportion blame for the violence on the armed opposition in the same way as it does on the government.
Churkin stressed that the key to resolving the Syrian crisis was "through an inclusive political process led by the Syrians themselves."
Wang Min, China's representative, said that the resolution amounted to undue interference in the affairs of a sovereign state, a position echoed by Bashar Jaafari, the Syrian representative to the UN.
The United Nations, Jaafari added, was in danger of being used by "some member states" as a way to provide cover for "armed terrorist groups."
But Susan Rice, the US ambassador to the UN, said the assembly had sent a "clear message" of support to the Syrian people.
"An overwhelming majority of U.N. member states have backed the plan put forward by the Arab League to end the suffering of Syrians," she said. "Bashar al-Assad has never been more isolated."
Earlier, Ban Ki-moon, the UN general-secretary, said crimes against humanity had probably been committed by Syrian forces, echoing concerns of Navi Pillay, the UN's human rights chief, who has called for the situation in Syria to be referred to the International Criminal Court.
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"We see neighbourhoods shelled indiscriminately, hospitals used as torture centres, children as young as 10 years old killed and abused. We see almost a certain crimes against humanity," Ban said during a visit to Austria.
Security forces attacked the central city of Homs for a twelfth straight day on Thursday, while 18 people were killed in central Hama province and four others in the southern city of Deraa, activists reported.
Al Jazeera's Rula Amin, reporting from Beirut in neighbouring Lebanon, said: "Syrian government forces seem to be on the offensive, pushing back into areas where the [opposition] Free Syrian Army had taken control in the past few weeks.
"They have been conducting severe seizures and bombardments in many areas in the country: Hama, Homs and suburbs of Damascus, and this morning in Deraa in the south."
There was no comment from Syrian authorities, who tightly restrict media access to the country.
Syrian security forces have continued their campaign even after Assad set February 26 as the date for a referendum on a new constitution, which the government says will lead to multi-party elections within 90 days.
The arrest of blogger Razan Ghazzawi, a symbol of the uprising against Assad's rule, and a prominent human-rights activist, Mazen Darwish, along with his wife and 11 others, was reported by the human-rights lawyer Anwar Bunni.
Bunni said Ghazzawi was arrested on Thursday in an early afternoon raid on the Syrian Centre for Media and Freedom of Expression, which is located in central Damascus and is headed by Darwish.
"We at the Syrian Centre for Legal Studies condemn these arrests and call on Syrian authorities to immediately release them," Bunni said in a statement.
The Paris-based watchdog, Reporters Without Borders, condemned the arrests and demanded the activists' immediate release.
In other developments on Thursday, the Syrian National Council (SNC) re-elected Burhan Ghalioun as president of the bloc. His mandate as leader of the coalition, which has become the main voice of the Syrian opposition, runs to April 15.
In-depth coverage of escalating violence across Syria
China, which drew global condemnation when it joined Russia in vetoing a Security Council resolution on Syria, said on Thursday it would send an envoy to Damascus to push for a "peaceful" end to the conflict.
Zhai Jun, the Chinese deputy foreign minister, will visit Syria from February 17 to 18, a foreign ministry spokesman said.
Russia and China have so far refused to yield to diplomatic pressure over Syria.
However, France said on Thursday that compromise with Russia at the Security Council was possible to end the violence in Syria in the short term, and that France was ready to work on a new resolution to provide humanitarian aid to Syrians.