Syrian forces backed by tanks killed at least 20 civilians in the city of Homs today in one of the fiercest military assaults on urban centres to crush six months of pro-democracy protests, activists and residents said.

Most of the killings occurred in old neighbourhoods of the city, situated on the main northern highway 165km from Damascus.

Districts such as Bab Sbaa and Bab Dreib and Bab Hut have seen the biggest daily protests to demand that president Bashar al-Assad step down, as their maze of streets help protesters escape from security forces, activists and residents said.

The head of the Arab League will visit Syria on Saturday to convey concerns over the bloody crackdown, a League official and Arab diplomats said today.

Arab League secretary-general, Nabil Elaraby, had originally been expected to travel to Damascus today. But Arab diplomats said the visit was delayed at Syria's request. No official explanation was given.

Arab governments broke months of silence over Syria at a meeting in Cairo last week, demanding an end to the bloodshed, and decided to send Mr Elaraby to Damascus to press for political and economic reforms.

An Arab diplomatic source said Damascus delayed the visit after Mr Elaraby met Syrian opposition members and because of a leaked Qatari proposal, which had not been adopted, for possible demands that Arab states would make to Syria.

A member of the Syrian opposition, Haitham al-Malih, told Al Jazeera television he was among a group that met Mr Elaraby at the Arab League headquarters in Cairo. It was not immediately possible to confirm such a meeting with League officials.

The Arab League, which groups 23 Arab states, confirmed on its website that Mr Elaraby would now visit Syria on Saturday.

A League official also said there would be an Arab ministerial meeting next Wednesday in Cairo to discuss a number of issues, including Syria.

A representative at the League said there was no plan to suspend Syria's membership in the Arab body, as happened with Libya in February after forces loyal to the now deposed Libyan leader Muammar Gaddafi assaulted protesters.

"No one is thinking till now about freezing Syrian membership in the Arab League because every Arab state is keen on stability in Syria," the representative said.

"All that Arab foreign ministers asked in the last meeting was to speed up the pace of reforms and stop the violence," he added.

A source at the League said the proposal for Arab demands on Syria drawn up by Qatar included a call for a multi-candidate presidential election in 2014 and forming a national unity government headed by a candidate acceptable to the opposition.

The proposal was not approved by League members.

Another diplomat said the meeting next Wednesday would discuss Syria, Palestinian issues and Somalia.

The Arab representative said tensions between Sudan and the newly independent South Sudan as well as the situation in Libya would also be on the agenda.

A member of Syria's opposition, Fahd al-Masri, told Reuters opponents of the Assad regime would hold a demonstration outside the headquarters of the Arab League in coming days, as part of efforts to raise their concerns to Arab states.

Leading Syrian opposition figures were due to meet Egyptian civil society groups, religious leaders and members of the media, he added.