* Group to demand access to "areas under siege"
* Says can supply aid within 48 hours
* Commits to preventing arms sales to Syria govt
(Adds details from updated draft)
By Dominic Evans
BEIRUT, Feb 24 (Reuters) - Western and Arab powers meeting in Tunis on Friday will demand Syrian authorities allow immediate access for aid to the cities of Homs, Deraa, Zabadani "and other areas under siege", according to an updated draft declaration obtained by Reuters.
The draft conclusion of the conference also calls on Damascus "immediately to cease all violence" and pledges to deliver humanitarian supplies within 48 hours if Syria "stopped its assault on civilian areas and permitted access".
The meeting in Tunisia, the country where the Arab Spring erupted more than a year ago, brings together foreign ministers from more than 50 countries in the first gathering of the "Friends of Syria" after almost a year of protests against the rule of President Bashar al-Assad.
The group includes the United States, European Union countries and Arab and Muslim nations. Russia and China, which have both vetoed measures against Damascus at the United Nations, are not attending.
Friday's meeting takes place amid a surge in government attacks on the city of Homs and mounting world outrage over violence that has claimed thousands of lives during the uprising against Assad's rule.
Activists say the army is blocking medical supplies to parts of Homs, where hospitals, schools, shops and government offices are closed. The International Committee of the Red Cross has been trying to get the government and rebel forces to agree daily two-hour ceasefires.
In the absence of plans for military intervention, ministers are likely to focus on humanitarian support, but the draft statement also commits countries to enforce sanctions aimed at pressuring Syrian authorities to halt the violence.
Those measures include travel bans, asset freezes, halting purchase of Syrian oil, ceasing investment and financial services relating to Syria, reducing diplomatic ties and preventing arms shipments to the government.
The draft praises the main opposition Syrian National Council (SNC), which will be present in Tunis, but falls short of a full endorsement, recognising it as "a legitimate representative of Syrians seeking peaceful democratic change".
In a pointed reference to the divisions between the SNC's mainly exile figures and the grassroots activists driving the protests against Assad, it commends the "courage and determination of Syrians on the ground, who are the vanguard of the Syrian people seeking freedom and dignity".
"The group agreed to increase it engagement with and practical support for the Syrian opposition," the statement said, without specifying what that support might entail.
The updated draft, which a diplomat said may still be altered, dropped an earlier passage which encouraged the Arab League to resume a much criticised monitoring mission suspended in January after violence escalated in Syria.
The latest version simply "noted" the Arab League's request to the United Nations Security Council to issue a resolution to form a joint Arab-U.N. peacekeeping force following a cessation of violation by the regime as outlined above".
(Editing by Andrew Heavens)