Canada is open to expanding its humanitarian aid to help Syrians caught in the midst of increasing violence, Foreign Affairs Minister John Baird said today, as more reports emerged of a growing refugee crisis.

"We are prepared in Canada to do more," he said. "The answer on doing more is yes, Canada can and wants to do more. Our government wants to do more."

Baird's comments came following a meeting in Ottawa with Syrian opposition figures and Syrian-Canadians.

"We had a significant discussion about the humanitarian needs, not just within Syria," he said.

Baird said Canada's current aid commitment — $8.5 million — is the third largest contribution by any donor country. But he noted that the situation has "deteriorated" recently.

"There's obviously significant needs in the medical area and significant need to help document the crimes that are being undertaken in the country," Baird said.

UNICEF launches emergency appeal

Almost 115,000 people — half of them children and youth — have fled Syria and are registered as refugees in Jordan, Lebanon, Turkey and Iraq.

UNICEF on Wednesday launched an emergency appeal in Canada to support its Syrian emergency efforts.

"The needs among children and families displaced by the violence of recent days are enormous, whether in food, water and sanitation, or other basic supplies," UNICEF Syrian representative Youssouf Abdel-Jelil said in a statement.

UNICEF has said it needs $39 million from donor countries to support its humanitarian efforts in the region. So far, it says it's still $23 million short. It says 1.5 million Syrians need help.

Human rights monitors estimate that 19,000 people have been killed since March 2011 as forces loyal to Syrian President Bashar al-Assad ruthlessly crack down on any opposition.

Turkey seals Syrian border to trucks

Meanwhile, Turkey sealed its border with Syria to trucks on Wednesday, cutting off a vital supply line to the embattled nation as fighting stretched into its fifth day in Aleppo, Syria's largest city.

By stopping trucking across the 911-kilometre border, the move deprives Syria of a main route for imports and exports. Rebels fighting the al-Assad regime generally move their weapons and material over the border through clandestine smuggling routes.

Hayati Yazici, the Turkish customs and trade minister, said the move came after rebels captured two border crossings between Syria and Turkey. Last week, dozens of Turkish trucks were either looted or burned when the rebels took the Bab al-Hawa crossing.

Clashes in commercial hub

In Syria, an alliance of rebel forces attacked Aleppo, Syria's commercial hub, on Saturday, infiltrating sympathetic neighbourhoods in the north and south and then gradually moving towards the historic old city at the centre, a UN world heritage site.

The Britain-based Syrian Observatory for Human Rights reported more than two dozen people killed in fighting yesterday in Aleppo and large numbers of people fleeing the southern neighbourhood of Sukkari Wednesday morning.

Activist video from Wednesday showed a burning police station in the southern neighbourhood of al-Kelassa, while gunfire could be heard ringing out in the background. The Associated Press cannot independently confirm events portrayed in such videos posted online.

Syrian forces, however, managed to quash a similar assault last week in the capital Damascus using heavy weapons including attack helicopters, which are now being deployed in Aleppo, according to local activists and residents. The government forces eventually overpowered the outgunned and outmanned rebels.

A new commander for the 300-member UN observer force, Lt. Gen. Babacar Gaye arrived late Tuesday in Damascus along with the UN official in charge of peacekeeping operations to hold a series of meetings to assess the prospects for a UN peace plan that is being widely ignored.

Syrian opposition activists said the country's ambassador to Cyprus and the most recent ambassador to the United Arab Emirates have defected. Syrian National Council spokesman Yassin al-Naggar in Qatar said Damascus' envoy to Cyprus, Lamia al-Hariri, has arrived in the Gulf nation's capital Doha.

Al-Hariri's husband, Abdel Latif Dabbagh, is the former Syrian ambassador to the UAE. SNC member Shadi al-Khesh in the Emirati capital Abu Dhabi said Dabbagh has also defected.