AMMAN,BEIRUT Feb 21 - Syrian government forces killed at least 16 people and wounded some 340 on Tuesday when they unleashed a heavy artillery barrage on a rebel-held district of the city of Homs, activists said.
The bombardment rained down as International Committee of the Red Cross officials tried to negotiate a halt to the fighting to allow them to bring aid to civilians suffering in horrendous conditions after 18 days of attacks on Homs.
In Damascus, security forces opened fire on demonstrators overnight, wounding at least four, activists said, in the latest sign that the 11-month uprising against President Bashar al-Assad was taking a grip on the capital as well as the provinces.
Western powers and the Arab League prepared for a meeting of the Friends of Syria contact group in Tunisia on Friday to pressure Assad to step down, while Russia and China backed Assad's own programme for reforms.
Russia said it would not attend the meeting because the Syrian government would not be represented. The Russian Foreign Ministry suggested the United Nations Security Council should send a special humanitarian envoy to Syria.
Activists said government forces launched the artillery attack on Homs after rebel fighters holding the opposition Baba Amro district blocked troops from entering.
Several shells are falling each minute, activist Nader al-Husseini told Reuters from the district, adding that two children were among the victims.
The London-based Syrian Network for Human Rights said at least 250 shells and rockets had hit Baba Amro since the morning and Syrian Airforce planes were flying reconnaissance missions.
Government forces backed by armour and under the control of Alawite officers, from the same minority sect as Assad, have been advancing on Baba Amro, a Muslim Sunni neighbourhood, since the offensive on Homs began on Feb 3. Tanks are deployed at the Inshaat district next to Baba Amro, opposition sources said.
Homs, a city of one million people strategically sited on the Damascus-Aleppo highway, has been at the heart of the uprising against Assad's 11-year-rule.
The dangerous conditions and government restrictions on access make it difficult for foreign media to verify details of the activist reports; but international rights and aid organisations confirm a bloody and desperate scenario in which several hundred people have been killed.
UNDER FIRE IN DAMASCUS
Undermining Assad's argument that the revolt is the work of foreign-backed terrorists and limited mainly to the provinces, crowds rallied in Damascus on Monday night, coming under fire from security forces. At least four people were wounded, activists said.
There were hundreds of demonstrators at the main square of Hajar al-Aswad and suddenly buses of security police and shabbiha (pro-Assad militia) turned up and started firing into the crowd, activist Abu Abdallah told Reuters by telephone.
Footage posted on YouTube, purportedly taken before the shooting, showed a crowd marching in Hajar al-Aswad carrying placards in support of besieged Homs and singing Eyes are shedding tears for the martyrs among Syria's youth.
Elsewhere, an activist group in Kfar Tkharim near the Turkish border said rebel fighters had killed five soldiers and captured two in an ambush on a government column.
Activists in the western city of Hama said troops, police and militias had set up dozens of roadblocks, cutting neighbourhoods off from each other.
Ahmad Ramadan, a leader of the opposition Syrian National Council, said Assad loyalists killed his brother Mahmoud when they riddled his car with gunfire in his home city of Aleppo.
The regime has been accusing Mahmoud of sending food and medicine to Homs and he was receiving daily threats. He was hit in the head and neck and died immediately, Ramadan told al-Jazeera Arabic news channel.
CALL FOR CEASEFIRE
The Geneva-based International Committee of the Red Cross, the only international organisation deploying aid workers in Syria, said it was in talks with the authorities and opposition fighters for a ceasefire to bring aid to civilians.
Diplomatic sources said it was seeking a two-hour ceasefire in hotspots including Homs, where residents are running out of food, water and medicine.
Western and Arab countries who want Assad to relinquish power are preparing an explicit gesture of support for his opponents.
U.S. Secretary of State Hillary Clinton said the Friends of Syria meeting in Tunisia would show that his government was increasingly isolated and offer support for the brave Syrian people.
We'll send a clear message to Russia, China and others who are still unsure about how to handle the increasing violence but are up until now unfortunately making the wrong choices, Clinton said in Mexico at a meeting of the G20 world powers.
Germany said the European Union would probably impose more sanctions against Syria in the coming week. Western sanctions have so far had little impact without support from Russia and China for measures at the U.N. Security Council.
Assad met a senior Russian politician in Damascus on Monday, who reiterated Moscow's support for his self-styled reform programme and spoke out against any foreign intervention. China accused Western countries of stirring up civil war.
Nevertheless, the Arab League, which has suspended Syria, said there were signs that Russia and China could temper their support for him.
There are indications coming from China and to some extent from Russia that there may be a change in position, League Secretary-General Nabil Elaraby said in Cairo.
Russia and China vetoed a draft U.N. Security Council resolution this month that would have backed an Arab plan calling for Assad to step down. The two countries also voted against a similar non-binding resolution in the General Assembly last week.
Assad's government says it is committed to meeting demands for democracy with a referendum on Sunday on a new constitution, leading to multi-party elections within 90 days.
The West and Syrian opposition figures have dismissed the plan as a joke, saying it is impossible to have a valid election amid the continuing repression.
(Additional reporting by Dominic Evans in Beirut, Dave Graham and Andrew Quinn in Los Cabos, Mexico, and Shaimaa Fayed in Cairo; Writing by Angus MacSwan in Beirut; Editing by xxx)