An Arab League observer has left Syria, accusing the authorities of committing war crimes and turning the Arab monitoring mission into a 'farce'.

'They didn't withdraw their tanks from the streets, they just hid them and redeployed them after we left,' Anwar Malek told Al Jazeera English television at its headquarters in Qatar, still wearing one of the orange vests used by the monitors.

'The snipers are everywhere shooting at civilians. People are being kidnapped. Prisoners are being tortured and no one has been released,' the Algerian former observer said. 'Those who are supposedly freed and shown on TV are actually people who had been randomly grabbed off the streets.'

The Arab League monitoring mission, now about 165-strong, began work on December 26. Its task is to verify if Syria is complying with an agreement to halt a crackdown on 10 months of protests against President Bashar Al-Assad in which the United Nations says more than 5,000 people have been killed.

Malek's resignation was the latest blow to a mission already criticised for inefficiency and whose members have come under attack this week from both Assad supporters and protesters.

'The mission was a farce and the observers have been fooled,' Malek said. 'The regime orchestrated it and fabricated most of what we saw to stop the Arab League from taking action against the regime.

'What I saw was a humanitarian disaster. The regime isn't committing one war crime but a series of crimes against its people,' he added.

Syria has barred most independent media, making it difficult to verify conflicting accounts of events on the ground. There was no immediate comment on his remarks from the Arab League, which decided on Sunday to keep the monitors in place at least until they report again on their mission on January 19.

Under the Arab peace plan, Syrian authorities are supposed to stop attacking peaceful protests, withdraw troops and tanks from the streets, free detainees and open a political dialogue.

Malek criticised the mission's leader, Sudanese General Mohammed al-Dabi, already under fire from human rights groups concerned about his past role in the conflict in Darfur.

'The head of the mission wanted to steer a middle course in order not to anger the (Syrian) authorities or any other side,' said Malek, who had earlier drawn attention for critical comments he posted on Facebook while still in Syria.

A UN official told the Security Council on Tuesday that Syria had accelerated its killing of protesters after the Arab monitors arrived, the US envoy to the United Nations said.

'The under-secretary-general noted that in the days since the Arab League monitoring mission has been on the ground, an estimated 400 additional people have been killed, an average of 40 a day, a rate much higher than was the case before their deployment,' ambassador Susan Rice told reporters in New York. - Reuters