BEIRUT — U.N. Secretary General Ban Ki-moon accused the Syrian regime of committing "almost certain" crimes against humanity Thursday as activists reported fresh violence and the arrest of several prominent dissidents, including a U.S.-born blogger.

Speaking to reporters in Vienna, Ban demanded the Syrian regime stop using indiscriminate force against civilians caught up in fighting between government troops and President Bashar Assad's opponents.

"We see neighbourhoods shelled indiscriminately," Ban told reporters in Vienna. "Hospitals used as torture centres. Children as young as ten years old jailed and abused. We see almost certain crimes against humanity."

Syrian activists said government forces attacked Daraa on Thursday, carrying out arrests and shooting randomly in the city where the uprising against Assad erupted 11 months ago. They also reported intense clashes between army defectors and government troops in the central province of Hama.

The push into Daraa, located near the Jordanian border some 80 miles (130 kilometres) south of Damascus, followed sieges on the rebellious cities of Homs and Hama and appears to be part of an effort by the regime to extinguish major pockets of dissent.

Also Thursday, the Local Coordination Committees, an umbrella group of activists, reported the arrest of a several activists, including Razan Ghazzawi, a U.S.-born blogger and press freedom campaigner.

Ghazzawi, who was born in Miami, Florida, was arrested early in the uprising and charged with spreading false information, but she was released after about two weeks.

The LCC said security forces also arrested leading human rights activist Mazen Darwish and others during a raid on their Damascus office. The reports could not be immediately confirmed.

The LCC said dozens of people were killed throughout the country Thursday.

Another activist group, the Britain-based Syrian Observatory for Human Rights, said security forces killed at least one civilian in Daraa, and that clashes between defectors and government troops there left at least three regime soldiers dead.

The deadliest fighting between troops and defectors took place in the village of Kfar Naboudeh in Hama province where government forces killed 10 defectors and four civilians, according to the Observatory. The group said the defectors attacked an army checkpoint near the Hama town of Soran, killing four soldiers.

Death tolls are all but impossible to confirm in Syria, which has banned independent reporting.

The Syrian revolt started in March with mostly peaceful protests against the Assad family dynasty, but the conflict has become far more violent and militarized in recent months as army defectors fight back against government forces.

The U.N. General Assembly scheduled a vote for Thursday on an Arab-sponsored resolution strongly condemning human rights violations by the Syrian regime and backing an Arab League plan aimed at ending the conflict.

Assembly spokeswoman Nihal Saad said Wednesday that the vote will take place Thursday afternoon. There are no vetoes in the 193-member world body and U.N. diplomats said the resolution, which already has 60 co-sponsors, is virtually certain to be approved.

While General Assembly resolutions are nonbinding, they do reflect world opinion on major issues and supporters are hoping for a high "yes" vote to deliver a strong message to Assad's regime.

On Wednesday, Assad ordered a Feb. 26 referendum on a new constitution that would create a multiparty system in Syria, which has been ruled by the same family dynasty for 40 years. Such a change would have been unheard of a year ago, and Assad's regime is touting the new constitution as the centerpiece of reforms aimed at calming Syria's upheaval.

But after almost a year of bloodshed, with well over 5,400 dead in the regime's crackdown on protesters and rebels, Assad's opponents say the referendum and other promises of reform are not enough and that the country's strongman must go.

Assad's call for a referendum also raises the question of how a nationwide vote could be held at a time when many areas see daily battles between Syrian troops and rebel soldiers.

The U.S. and France dismissed the referendum move as an empty gesture.

"How can he propose a referendum ... while continuing to shoot cannons at the innocent population at the centre of some Syrian cities," French Foreign Minister Alain Juppe told journalists Thursday in Vienna.

He added that France is working at the United Nations on a resolution inspired by the Arab League proposal that calls on Assad to hand power to his vice-president.

In Washington, U.S. State Department spokeswoman Victoria Nuland said that Assad "knows what he needs to do if he really cares about his people."

"The violence just needs to come to an end, and he needs to get out of the way so we can have a democratic transition," she told reporters

In Strasbourg, the speaker of the European Parliament said Assad's leadership was "completely discredited" and that his proposal to submit a new constitution to a referendum before a nation at war is "inconceivable."

"The European Parliament wants to see humanitarian corridors to be put into place and shelters provided for the growing numbers of displaced people," Martin Schulz said. "The parliament urges the EU ... to help strengthening the unity of the Syrian forces which oppose the regime inside and outside the country."

Russia, a top Syrian ally, has presented Assad's reform promises as an alternative way to resolve Syria's bloodshed. Earlier this month, Moscow and Beijing vetoed a Western- and Arab-backed resolution at the U.N. Security Council aimed at pressuring Assad to step down.

Chinese Vice Foreign Minister Zhai Jun will be in Syria on Friday and Saturday for talks on how to end the violence, Foreign Ministry spokesman Liu Weimin said Thursday. Zhai met a Syrian opposition delegation in Beijing last week.

"I believe the message of this visit is that China hopes for a peaceful and proper resolution of the Syrian situation, and that the Chinese side will play a constructive role in the mediation," Liu said.

On Thursday, the Britain-based Syrian Observatory for Human Rights reported raids and shooting by Syrian troops in Daraa, along with renewed shelling in the rebellious neighbourhood of Baba Amr in Homs.

Homs has seen one of the deadliest assaults of the crackdown that activists say has killed hundreds in the past two weeks, aimed at crushing a city that has been a stronghold of dissent.