Turkey has called the violence in Syria "a crime against humanity" on the scale of the 1990s bloodshed in the Balkans, as a Red Cross convoy was once again barred from entering the Homs suburb of Baba Amr.

The comment by Turkish foreign minister Ahmet Davutoglu follows similar remarks from the EU on Friday, which called for the documentation of war crimes in Syria.

"No government, no authority, under no circumstances, can endorse such a total massacre of its own people," Davutoglu said. "The international community must speak louder. The lack of international consensus is giving Syria the courage to continue."

The criticism came at the end of a week in which the UK and France closed their embassies in Syria, and China and Russia appeared to shift position in calling for President Bashar al-Assad's regime to admit UN humanitarian chief Valerie Amos.

"The situation in the field seems to resemble Sarajevo or Srebrenica. This seems to be the way we are heading," Davutoglu said at a joint news conference with Giulio Terzi, Italy's foreign minister. "We believe that diplomatic pressure on the Assad regime must be increased. We say this not only from the point of view of the EU. We believe all international institutions must do this."

China urged the government and the rebels to immediately end all acts of violence, especially against civilians. A foreign ministry statement urged both sides to "launch an inclusive political dialogue with no preconditions" under the mediation of former UN secretary- eneral Kofi Annan, the newly appointed UN-Arab League envoy on the Syria crisis, .

On Friday, current UN secretary general Ban Ki-moon said he had received "grisly reports" that Assad's troops were executing, imprisoning and torturing people in Homs. Syrian forces continued to pound the battered city and authorities handed over the bodies of two journalists killed in Baba Amr last month – including Marie Colvin of the Sunday Times – to diplomats in Damascus.

Meanwhile, the wounded French journalist Edith Bouvier described for the first time how she feared her attempt to escape from Homs had ended inside a dark, three-kilometre tunnel that rebels were using to supply the besieged district of Baba Amr when the Syrian army bombarded its exit.

Bouvier was abandoned, taped to a stretcher with a broken leg, as rebels and dozens of wounded headed back to the neighbourhood. "One of them placed his Kalashnikov on me. He put his hand on my head and said a prayer. It wasn't very reassuring. Then he left," Bouvier told Le Figaro newspaper, for which she was working in Syria. "I didn't know what was going to happen. Was the exit blocked? Were Syrian soldiers going to enter? I wanted to run away, before remembering that I was taped to a stretcher." Bouvier and French photographer William Daniels, who stayed with her, were finally rescued by a rebel who drove down the tunnel on a motorbike.

Concern was mounting for civilians in freezing conditions in battered Baba Amr, where trucks from the International Committee of the Red Cross (ICRC) were still blocked from entering. "The ICRC and Syrian Red Crescent are not yet in Baba Amr today. We are still in negotiations with authorities. It is important that we enter today," ICRC spokesman Hicham Hassan said.

Anti-government activists said they feared troops were keeping out the ICRC to prevent aid workers witnessing a massacre. UN chief Ban blamed Damascus for the fate of civilians. "The brutal fighting has trapped civilians in their homes, without food, heat or electricity or medical care; without any chance of evacuating the wounded or burying the dead. People have been reduced to melting snow for drinking water. This atrocious assault is all the more appalling for having been waged by the government itself, systematically attacking its own people."

Bashar Ja'afari, Syria's UN ambassador, said Ban's remarks included "extremely virulent rhetoric which confines itself to slandering a government based on reports, opinions or hearsay".

Elsewhere in the country, Syrian state news agency Sana said a suicide car bomber in the town of Deraa, near the border with Jordan, had killed two people and wounded 20. Residents claimed seven people had been killed, and anti-Assad activists denied the attack was a suicide bombing. Rami Abdelrahman, head of the Britain-based Syrian Observatory for Human Rights, said anti-Assad fighters had earlier killed six soldiers and wounded nine in al-Herak.