The United Nations Security Council urged Syria to halt a humanitarian crisis taking place in the country, a statement said on Thursday, which was also signed by long-time Syria backers Russia and China.

In the missive, UNSC members said they "deplore" a rapidly humanitarian crisis, urging Syrian authorities to allow UN humanitarian aid chief Valerie Amos to visit the country.

The joint statement came after the Red Cross indicated that the regime of Syrian President Bashar Assad finally allowed its officials to enter the war-torn Homs area, after rebel forces withdrew from the site of the weeks-long battle.

Russia, China and Cuba voted against a resolution adopted overwhelmingly by the Geneva-based UN Human Rights Council which condemned Syria for violations that may amount to crimes against humanity.

Earlier Thursday, activists indicated that most Syrian rebels pulled out of the besieged Baba Amro district of Homs after a 26-day siege by Assad's forces.

They said a few fighters had remained behind in the shattered quarter to cover the "tactical withdrawal" of their comrades.

Syrian forces again shelled Baba Amro earlier in the day, despite world alarm at the plight of civilians trapped there.

Snow blanketed the city, slowing a ground assault begun on Wednesday, but also worsening the misery of residents short of food, fuel, power, water and telephone links, activists said.

Reports from the city could not be verified immediately due to tight government restrictions on media operations in Syria.

Assad is increasingly isolated in his struggle to crush an armed insurrection that now spearheads a year-long popular revolt against four decades of his family's iron-fisted rule.