Washington: Syria's army and its Russian and Iranian allies are closing in on rebel strongholds in the country's north in an advance that has already derailed peace talks and may also unleash a new wave of refugees into Europe.
The military forces of President Bashar al-Assad, supported by Russian air power and Iran-backed Hezbollah militants, are only about three kilometres away from Aleppo, once the country's most populous city, Rami Abdulrahman, head of the British-based Syrian Observatory for Human Rights, said by phone.
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Assad forces gain ground in Aleppo
Syrian soldiers enter the towns of Nubl and al-Zahraa near Aleppo, potentially cutting off rebel forces from their supply lines in Turkey.
Their breakthrough threatens to cut off the rebel forces there from supply lines to Turkey. The United Nations on Wednesday suspended its long-awaited peace conference in Geneva just days after it began, as opposition groups called for international pressure to halt the government advance.
For leaders gathered at a separate meeting in London to discuss aid to Syria, the intensification of fighting is ominous because it could add to the mass exodus of refugees that is already destabilising several European countries.
Turkish Prime Minister Ahmet Davutoglu, speaking in London on Thursday, said as many as 70,000 Syrians were already on their way to Turkey from northern Aleppo, and warned of a wider humanitarian disaster if Aleppo falls. The SOHR said about 40,000 people have fled the region in the past few days.
The number could surpass could surpass 100,000 if the rebels can't regain control of supply route between Aleppo and Azaz, near the Turkish border, cut off by heavy bombardment by Russian warplanes, said Mehmet Emin Arslan, an official at the Humanitarian Aid Foundation in Turkey's Gaziantep province, near the Syria border.
The European leaders in London are seeking an increase in aid that will improve conditions in camps and convince refugees not to risk sea and land journeys to reach European Union countries.
"The German government is convinced that the great migration of refugees can only be resolved by addressing its root cause in the region," German Chancellor Angela Merkel, under intense pressure at home to act after more than 1 million asylum seekers made their way to Germany last year, said at the conference. The meeting is a "significant building block in coming closer to this goal, when one thinks of Syria and its neighbours", she said.
Taking Aleppo, Syria's former commercial hub, would give Russia, Iran and Mr Assad more bargaining power at any future settlement talks and more say in how the region will be redefined. It would also exacerbate tensions with Turkey, which supports the ouster of Mr Assad and last year shot down a Russian fighter plane it said crossed into its territory during operations over Syria.
A siege of the city and capture of the northern supply line "would effectively diminish Turkey's say over the war in Syria, while leaving it exposed to a growing refugee crisis", Nihat Ali Ozcan, an analyst at the Economic Policy Research Foundation of Turkey, an Ankara-based think tank, said by phone.
Biden: US ready to use force against IS in Syria
After meeting Turkish Prime Minister Ahmet Davutoglu, US Vice-President Joe Biden says the two countries are ready for a military solution against IS if a political settlement in Syria is not possible.
Russia warned on Thursday that Turkey may be preparing to intervene militarily to stop that from happening. The Russian Defence Ministry said it has "reasonable grounds" to suspect Turkey of "intensive preparations" for sending troops into Syria, though there was no immediate evidence of that on the Turkish side.
A civil war that has killed 250,000 people over five years and forced millions of others to flee their homes has confronted Europe with the rising threat of terrorism as well as a growing migrant crisis. Turkey, a candidate to join the European Union, is home to the largest Syrian refugee population, and the EU has offered a €3 billion ($4.6 billion) aid package to encourage Turkey to keep refugees from heading west.
According to the UN, there are also 2.1 million Syrian refugees registered in Lebanon, Jordan, Iraq and Egypt. The UN says $US7.7 billion ($10.9 billion) is needed this year to fund shelters for the refugees. According to British Prime Minister David Cameron, $US5.6 billion has been pledged for 2016 with a further $US5.1 billion committed for the following four years.
UN Secretary-General Ban Ki-moon said the sums raised at the London conference were the largest ever for an event addressing a single crisis. "Offering hope is the best way to slow the exodus of educated Syrians and prevent the radicalisation of a lost generation," Mr Ban said.