Syrian troops killed 20 civilians and arrested dozens yesterday, a rights watchdog said, a day after Damascus pledged to withdraw its forces from protest hubs under a deal with the Arab League to end months of bloodshed.

The Syrian Observatory for Human Rights said the victims fell in various neighbourhoods of the flashpoint protest city of Homs, in central Syria, where government forces reportedly used heavy tank-mounted machineguns.

EU foreign policy chief Catherine Ashton joined world leaders in welcoming the Arab deal and urging Syria to comply quickly with the terms.

But activists remained sceptical and called for mass demonstrations on Friday to test the government’s commitment to the peace deal while the largest opposition group met Arab League chief Nabil al-Arabi to voice its concerns.

“We told the secretary general of our fears that the regime will not keep its promises,” Samir al-Nashar, a member of the opposition Syrian National Council, said in Cairo.

Mr Arabi briefed them on the peace plan, which also calls on Syrian President Bashar al-Assad to engage in a national dialogue with his opponents, said Mr Nashar, adding that the SNC does not want talks but for Assad to quit.

“We are not talking about a dialogue. We offered to engage in negotiations to move from a authoritarian regime to a democratic regime. And we ask that Mr Bashar al-Assad resign.”

The SNC is the largest and most representative Syrian opposition grouping. On Wednesday it urged the Arab League to freeze Syria’s membership in the 22-strong organisation and recognise it as the sole representative of the opposition.

Assad’s opponents are sceptical about the regime’s readiness to rein in a brutal crackdown that the United Nations says has cost more than 3,000 lives since mid-March.