Ban slams Assad for crimes on humanity as US, Russia meet

He added that the UN inspector's report into the incident would provide a confirmation of the usage of chemical weapons

UN chief Ban Ki-moon has accused Bashar al-Assad of crimes against humanity as complex, high-stakes talks between the US and Russia on dismantling Syria's chemical weapons arsenal reached a pivotal point, stretching late into the night.

US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov were holding a second day of talks in Geneva to hammer out the details of a Russian plan to bring the weapons under international control that emerged this week.

All day the top diplomats plus their delegations shuttled in and out of meetings, breaking up into smaller technical teams, and then rushing back to consult with their governments. As both sides hailed the talks as "constructive," they confirmed the talks were looking likely to stretch into today.

Teams of experts have been poring over a last-minute Russian initiative which caused US President Barack Obama to back away from planned military strikes in response to an August chemical attack near Damascus, which Washington blames on the regime and says killed about 1,400 people.

At the United Nations, Ban yesterday lashed out at Assad and said a UN inspectors' report into the incident would provide "overwhelming" confirmation that chemical weapons were used.

The Syrian leader President Bashar al-Assad had "carried out many crimes against humanity," Ban said, and insisted there had to be "accountability" once Syria's civil war is over.

The two sides "made progress in coming closer to agreement on the scope of the chemical weapons stockpile," a senior US administration official said.

The US has estimated that Syria possesses around 1,000 metric tonnes of various chemical agents, including mustard and sarin gas, sulfur and VX.

The Russian estimates had been initially much lower, the official said, without giving a figure.

"It's the same questions of what is it, where is it, how do we track it down, can we account for it, those are all part of the discussions," said a senior State Department official.

"We're obviously at a pivotal point."

Washington and Moscow were also "working hard to find common ground" to get peace talks going in Geneva that would bring together Assad's regime and the opposition and end the war which erupted in March 2011, Kerry said earlier.