An aid convoy has been refused access to Baba Amr district of Homs, where residents have been without water for the last four days. Elsewhere in Syria, there have been anti-government protests following Friday prayers. Human rights campaigners claim that 13 people were killed when troops fired a mortar into a crowd of demonstrators in the town of Rastan. Britain's Channel Four News correspondent Carl Dinnen reports.
The Red Cross told Syria on Friday it was unacceptable that its aid convoy had been prevented from entering a battle-scarred district of Homs where the opposition said President Bashar Assad's army had committed a massacre.
Baba Amr became a symbol of resistance to Assad after government troops surrounded it with tanks and artillery and shelled it intensively for weeks, killing and wounding civilians cowering in its ruined buildings.
"It is unacceptable that people who have been in need of emergency assistance for weeks have still not received any help," ICRC President Jakob Kellenberger said in a statement.
"We are staying in Homs tonight in the hope of entering Baba Amr in the very near future."
A convoy of trucks with food and other aid was preparing to enter the shattered district of Baba Amr, the International Committee of the Red Cross, or ICRC, said Friday.
The ICRC received a "green light" from Syrian authorities late Thursday, hours after rebels left the heavily bombarded area following a 26-day siege aimed at crushing a symbol of the revolt against President Assad.
Rebels withdrew on Thursday in a key moment in the year-old uprising against Assad's rule. An official at Syria's Ministry of Foreign Affairs and Expatriates said the army had "cleansed Baba Amr from the foreign-backed armed groups of terrorists."
Activists said Syria's army was hunting down and killing insurgents who had stayed to cover their comrades' retreat, although the reports could not be verified. They said 10 young men were shot dead on Friday.
U.N. Secretary-General Ban Ki-moon made an impassioned plea on Friday for Damascus to grant immediate access for aid workers to besieged Syrian towns, describing the images of death coming out of the country as atrocious.
"The images which we have seen in Syria (are) atrocious," Ban told reporters. "It's totally unacceptable, intolerable. How as a human being can you bear ... this situation? That really troubles me. I'm deeply sad seeing what's happening."
In a rare show of unity with Western powers, Russia and China joined other U.N. Security Council members on Thursday in expressing "deep disappointment" at Syria's failure to allow the U.N. humanitarian aid chief Valerie Amos to visit the country, and urged that she be allowed in immediately.
Russia and China have twice vetoed council resolutions that would have condemned Syria for the crackdown and demanded that it halt the crackdown on anti-Assad demonstrators.
The United Nations says Syrian security forces have killed more than 7,500 civilians during the government crackdown on pro-democracy protesters.
"All violence must stop," said Ban. "I am really urging Syrian authorities to stop (the) violence and allow humanitarian access."
With government forces moving in, the U.N. human rights office voiced dismay over reports suggesting former rebel areas were being subjected to bloody reprisals.
Syrians flee into limbo in northern Lebanon
"We are alarmed at reports starting to come out of the Baba Amr district of Homs after it was taken over by government forces yesterday (Thursday)," U.N. human rights spokesman Rupert Colville told a news briefing in Geneva.
"Although we are not, at this point, in a position to confirm any of those reports, we would like to remind the authorities of their responsibilities under international law.
UN demands immediate 'unhindered' humanitarian access to Syria
"It is essential," Colville added, "that there are no unlawful reprisals, no summary executions, no torture, no arbitrary detention. And the rights of those who are detained must be respected."
Britain's prime minister David Cameron told a press conference in Brussels that "the history of Homs is being written in the blood of its own people" and that the city "is a scene of medieval barbarity."
His concerns were echoed by French president Nicolas Sarkozy, who said France had closed its embassy in Damascus.
Snow delays convoy
ICRC spokesman Hicham Hassan said a joint ICRC and Syrian Arab Red Crescent team, carrying seven truckloads of food and other aid, that left Damascus on Friday morning had faced a weather delay.
"Snow is making the movement of the convoy slower, but we hope to be in Homs within the hour. Red Crescent volunteers and ambulances are waiting in Homs for the convoy to arrive and we are hoping to enter Baba Amr as soon as possible," he said.
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Ayman Mohyeldin, NBC News correspondent in Lebanon, Reuters and msnbc.com staff contributed to this report.