Mohammed Saeed, an Aleppo-based activist, said helicopters were firing with heavy machine-guns on rebel-held areas east and west of the city on Friday. He added that army reinforcements arrived in the city on Thursday and a major attack is expected any time.
U.N. High Commissioner for Human Rights Navi Pillay said unconfirmed reports are coming out of the capital, Damascus, of extra-judicial killings and shootings of civilians during fighting in the city's suburbs. Pillay said the report "bodes ill for the people of that city (Aleppo)."
Pillay said she believes President Bashar Assad's regime and opposition forces are both committing crimes against humanity and war crimes.
"And it goes without saying, that the increasing use of heavy weapons, tanks, attack helicopters and reportedly even jet fighters in urban areas has already caused many civilian casualties and is putting many more at grave risk," she said in a statement read aloud to reporters by her spokesman Rupert Colville.
Pillay said there is a pattern of government forces trying to clear areas that it says are occupied by opposition forces. There has been an accompanying rise in the number of reports of opposition fighters torturing or executing prisoners, she said.
A senior U.N. diplomat close to the mediation effort of international envoy Kofi Annan said they are "watching the situation in Aleppo with great concern."
"The ground is shifting. We use words like 'It's fluid' and it certainly is ... It has been a roller-coaster ride," the diplomat said, while speaking on condition of anonymity because of the delicacy of the negotiations among world powers on the U.N. Security Council. "While we are trying to apportion blame (for the diplomatic standoff), people are dying. Kids are being slaughtered."
The International Committee of the Red Cross said Friday it is temporarily moving some of its foreign staff from Damascus to neighboring Lebanon. A Red Cross spokesman in Geneva, Hicham Hassan, said the move was prompted by security concerns but that a core team of about 50 staff would remain.
Hassan also told The Associated Press that the Syrian Arab Red Crescent was suspending some of its operations in Aleppo due to heavy fighting.
"It's due to the deteriorating security situation in Damascus," he said. "This in no way means we are suspending our activities, especially at a time when needs are growing. ... They will go back to Damascus at the appropriate time."
About half of the 1.5 million people in need of humanitarian aid in Syria are children and adolescents, UNICEF spokesman Patrick McCormick told reporters Friday in Geneva. The U.N. children's agency, with the help of Syrian Arab Red Crescent and other groups, he said, has delivered food baskets, high protein biscuits and other items to 190,000 people, including 145,000 children, since January.
McCormick said they also have vaccinated a half-million Syrian children again polio and tuberculosis, but many of the children in refugee families are hungry and have lost a year of schooling and need medical and psychological care.
Warsaw also announced that it had closed its embassy and evacuated its diplomats from Damascus due to the deteriorating security situation. Poland's embassy had been representing U.S. interests in the Syria since the U.S. closed its own in February.
Turkey's state-run agency said a Syrian legislator from Aleppo has fled to Turkey and also warned that Syria was preparing for a massive offensive on cities where rebels are fighting government forces. The Anadolu agency said Friday that Ikhlas Badawi has defected in protest of the Syrian regime's "violence against the people."
She would be the first member of Syria's new parliament that was elected in May to defect.
In January, Legislator Imad Ghalioun left the country to join the opposition, saying Syria was suffering sweeping human rights violations. He was from the city of Homs that was being subjected to a massive regime attack at the time.
On Friday, the Britain-based Syrian Observatory said troops bombarded the Aleppo neighborhood of Fardous, killing at least four people. It added that a Sunni cleric, Abdul-Latif al-Shami, was kidnapped and killed in Aleppo. It gave no further details, although some activists said al-Shami is a government supporter.
Besides the violence in Aleppo, regime forces also shelled the central city of Homs, the northern town of Maaret al-Numan, the southern city of Daraa, and Damascus suburbs, the Observatory said, citing a network of sources on the ground.