27 July 2012 Last updated at 04:15 ET
Syrian rebels are readying themselves to battle government forces for control of Aleppo
Continue reading the main story
Syrian forces have renewed their assault on the northern city of Aleppo, firing from helicopter gunships on rebel-held areas.
The US state department has said it fears Syrian government forces are preparing to carry out a massacre.
The pro-government al-Watan newspaper has warned that the mother of all battles is about to start.
Rebels in Aleppo, Syria's most populous city, have been stockpiling ammunition and medical supplies in preparation.
Syrian troops fired from helicopter gunships on south-western neighbourhoods of Aleppo, the Syrian Observatory for Human Rights told the AFP news agency.
Continue reading the main story[h=2]At the scene[/h]
Ian Pannell BBC News, outside Aleppo
It is almost inconceivable that President Assad could allow his government to lose control of Aleppo, so it is reasonable to expect they are going to throw everything they possibly can at the city.
And that is what they are preparing for here. One of the neighbourhoods is appealing for more blood supplies. We are hearing reports of hundreds, possibly thousands of families leaving some districts. Everybody is bracing themselves for an intensive campaign.
The way it has worked in other cities is that there is an intensive bombardment by artillery and mortars, and then when it starts to go calm, tanks begin to roll in. This is a very congested heavily populated area, so it will be bloody.
A convoy of tanks from Idlib province, near the border with Turkey, arrived in Aleppo overnight and was attacked by rebels, the Observatory said.
At least 34 people were killed in the city on Thursday, activists said, as artillery and helicopter gunships attacked rebel targets.
Residents fleeThe US state department said the deployment of tanks, helicopter gunships and fixed-winged aircraft around Aleppo suggested an attack was imminent.
But the US would not intervene, said state department spokeswoman Victoria Nuland, except by continuing to channel non-lethal assistance such as communications equipment and medical supplies to the rebels.
The BBC's Ian Pannell, near Aleppo, says thousands of people have already left as fears grow that an intense battle looms.
Talal al-Mayhani, an activist with connections to the rebel movement in Aleppo, said the battle for the city was likely to play out in a similar way to an earlier battle in the capital Damascus.
There, rebels took control of large parts of the city before being forced to withdraw in the face of a government offensive.
Foreign journalists operate under heavy restrictions in Syria so claims made by either side are difficult to verify.
Continue reading the main story'Lessons from Balkans conflict'A Syrian MP from Aleppo has fled to Turkey, Turkey's state-run Anatolia news agency says.
Ikhlas Badawi, a mother of six, said she was defecting in protest at the "violence against the people".
Meanwhile, another defector, Gen Manaf Tlas, has put himself forward as a possible figure to unite the fractious opposition.
In an interview with a Saudi newspaper, Asharq al-Awsat, he said: "I am discussing with... people outside Syria to reach a consensus with those inside."
However, some in the opposition regard Gen Tlas - who fled earlier this month - as a compromised figure too close to the government of President Bashar al-Assad.
UN Secretary General Ban Ki-Moon said the world must apply the lessons learned from the Bosnian conflict in the 1990s.
He was speaking in Srebrenica, where a UN peacekeeping force failed to stop the killing of more than 7,000 Bosnian Muslim men and boys in 1995.
"I do not want to see any of my successors, after 20 years, visiting Syria, apologising for what we could have done now to protect the civilians in Syria - which we are not doing now," Mr Ban said.
The head of UN peacekeeping operations, Herve Ladsous, defended the decision to reduce the number of observers in Syria.
"We found ourselves with too many people and not enough to do," he said.
Speaking in Damascus, he said there was "no plan B" beyond Joint Special Envoy Kofi Annan's peace plan.
Repeated diplomatic attempts to stop the violence have foundered, with the UN Security Council bitterly divided.
The Syrian government has said its forces are trying to dislodge the "remnants of mercenary terrorist groups".
More than 16,000 people have been killed in Syria since the start of anti-regime protests in March 2011, activists say.
Continue reading the main story
Syrian forces have renewed their assault on the northern city of Aleppo, firing from helicopter gunships on rebel-held areas.
The US state department has said it fears Syrian government forces are preparing to carry out a massacre.
The pro-government al-Watan newspaper has warned that the mother of all battles is about to start.
Rebels in Aleppo, Syria's most populous city, have been stockpiling ammunition and medical supplies in preparation.
Syrian troops fired from helicopter gunships on south-western neighbourhoods of Aleppo, the Syrian Observatory for Human Rights told the AFP news agency.
Continue reading the main story[h=2]At the scene[/h]
It is almost inconceivable that President Assad could allow his government to lose control of Aleppo, so it is reasonable to expect they are going to throw everything they possibly can at the city.
And that is what they are preparing for here. One of the neighbourhoods is appealing for more blood supplies. We are hearing reports of hundreds, possibly thousands of families leaving some districts. Everybody is bracing themselves for an intensive campaign.
The way it has worked in other cities is that there is an intensive bombardment by artillery and mortars, and then when it starts to go calm, tanks begin to roll in. This is a very congested heavily populated area, so it will be bloody.
A convoy of tanks from Idlib province, near the border with Turkey, arrived in Aleppo overnight and was attacked by rebels, the Observatory said.
At least 34 people were killed in the city on Thursday, activists said, as artillery and helicopter gunships attacked rebel targets.
Residents fleeThe US state department said the deployment of tanks, helicopter gunships and fixed-winged aircraft around Aleppo suggested an attack was imminent.
But the US would not intervene, said state department spokeswoman Victoria Nuland, except by continuing to channel non-lethal assistance such as communications equipment and medical supplies to the rebels.
The BBC's Ian Pannell, near Aleppo, says thousands of people have already left as fears grow that an intense battle looms.
Talal al-Mayhani, an activist with connections to the rebel movement in Aleppo, said the battle for the city was likely to play out in a similar way to an earlier battle in the capital Damascus.
There, rebels took control of large parts of the city before being forced to withdraw in the face of a government offensive.
Foreign journalists operate under heavy restrictions in Syria so claims made by either side are difficult to verify.
Continue reading the main story'Lessons from Balkans conflict'A Syrian MP from Aleppo has fled to Turkey, Turkey's state-run Anatolia news agency says.
Ikhlas Badawi, a mother of six, said she was defecting in protest at the "violence against the people".
Meanwhile, another defector, Gen Manaf Tlas, has put himself forward as a possible figure to unite the fractious opposition.
In an interview with a Saudi newspaper, Asharq al-Awsat, he said: "I am discussing with... people outside Syria to reach a consensus with those inside."
However, some in the opposition regard Gen Tlas - who fled earlier this month - as a compromised figure too close to the government of President Bashar al-Assad.
UN Secretary General Ban Ki-Moon said the world must apply the lessons learned from the Bosnian conflict in the 1990s.
He was speaking in Srebrenica, where a UN peacekeeping force failed to stop the killing of more than 7,000 Bosnian Muslim men and boys in 1995.
"I do not want to see any of my successors, after 20 years, visiting Syria, apologising for what we could have done now to protect the civilians in Syria - which we are not doing now," Mr Ban said.
The head of UN peacekeeping operations, Herve Ladsous, defended the decision to reduce the number of observers in Syria.
"We found ourselves with too many people and not enough to do," he said.
Speaking in Damascus, he said there was "no plan B" beyond Joint Special Envoy Kofi Annan's peace plan.
Repeated diplomatic attempts to stop the violence have foundered, with the UN Security Council bitterly divided.
The Syrian government has said its forces are trying to dislodge the "remnants of mercenary terrorist groups".
More than 16,000 people have been killed in Syria since the start of anti-regime protests in March 2011, activists say.