Turkish Prime Minister Ahmet Davutoglu on Wednesday slammed as "hypocritical" calls by some countries urging Ankara to open its borders to Syrian refugees while failing to demand Russia halts punishing air strikes.

Turkey is under mounting pressure to open its border to people fleeing a Russian-backed assault by the Syrian regime of President Bashar al-Assad in the north of the war-torn country.

On a visit to the Netherlands, Davutoglu insisted the borders of his country had always been open to those fleeing Syria's civil war. Turkey already hosts some 2.5 million Syrian refugees.

"I find it hypocritical that some circles are telling Turkey to 'open your borders' while at the same time failing to tell Russia 'enough is enough'," Davutoglu told reporters.

But he added: "We will take in Syrians who want to come (to Turkey), but as a priority we are building a new camp to accommodate Syrians inside Syria's borders."

Tens of thousands of Syrians were still stranded Wednesday at the frontier north of the second city of Aleppo, where more than 500 people are said to have been killed in the offensive since February 1.

The Turkish leader also claimed that what was happening in Aleppo was "ethnic cleansing... with the goal of only leaving those behind who support the regime."

"Human rights and the Geneva Convention are being trampled underfoot," he said, adding "everyone must share the responsibility to combat this humanitarian disaster."

Dutch Prime Minister Mark Rutte also slammed the Russian air strikes, launched by Moscow late last year.

"The Netherlands calls on all parties including Russia to strictly comply with UN resolution 2254," he said.

Fighting must stop to allow "in humanitarian aid," Rutte said, adding the "Russian air strikes would seem to be in conflict with" the resolution.

Meanwhile, the Dutch parliament on Wednesday voiced broad support for airstrikes in Syria.

Rutte announced late last month that current bombing operations will be expanded from Iraq into its war-torn neighbour after the Netherlands received a request to join the US-led campaign.

New diplomatic talks on Syria are due to be held in Munich on Thursday to discuss providing humanitarian relief to Aleppo and other cities besieged by the Russian-backed regime forces.

Russia is a signatory to UN Security Council resolution 2254, passed in December, which orders all warring parties in Syria to respect an immediate ceasefire and allow humanitarian access to besieged civilians.

Turkey was the main gateway for the more than one million migrants and refugees who crossed into Europe last year most fleeing the war in Syria, and has come under pressure from the European Union to do more to stop them entering into the EU.

The problem shows no sign of slowing, and last week the EU thrashed out ways of financing a 3.0 billion euros deal with Turkey to help care for those already on its soil while stemming the flow of refugees.

Davutoglu insisted all the money would go towards helping the refugees and not be used for Turkey's own national interests.

Turkey had already spent some 10 billion euros on hosting just those refugees in camps, he said, warning the total cost for all refugees was between 20 to 25 billion euros.