ISTANBUL - Twenty-four migrants, including 11 children, drowned in the Aegean Sea on Monday as they tried to cross from Turkey to Greece, Dogan news agency said.

The agency initially said at least 35 migrants had died in two separate accidents off western Turkey, but later reported that there was a single incident with 27 deaths.

The migrants died when their boat sank off the district of Edremit in the western province of Balikesir in an apparent bid to reach the Greek island of Lesbos, Dogan said. Two were rescued both by air and by sea in a search and rescue operation by the Turkish coastguard, Dogan news agency said. Twelve were still missing.

Turkey, which is hosting at least 2.5 million refugees from Syria's civil war, has become the main launchpad for migrants fleeing conflict, persecution and poverty to Europe. The deaths came as German Chancellor Angela Merkel was meeting Turkish officials in Ankara for talks on reducing the influx of migrants to Europe.

The Turkish government struck a deal with the EU in November to halt the outflow of refugees, in return for three billion euros ($3.2 billion) in financial assistance. The EU on Wednesday finally reached an agreement on how to finance the deal. But the deal and the onset of winter do not appear to have deterred the migrants, with boats still arriving on the Greek islands daily.

The International Organization for Migration (IOM) said the number of refugees and migrants who perished in the Mediterranean in January alone topped 360. In January, almost 62,200 migrants and refugees entered Europe through Greece, according to the IOM, most of them from Syria, Afghanistan and Iraq. Turkish President Tayyip Erdogan threatened in November to flood Europe with migrants if European Union leaders did not offer him a better deal to help manage the Middle East refugee crisis, a Greek news website said on Monday.

Publishing what it said were minutes of a tense meeting last November, the financial news website revealed deep mutual irritation and distrust in talks between Erdogan and the EU's two top officials, Jean-Claude Juncker and Donald Tusk.

Meanwhile, Germany and Turkey said Monday they would ask NATO to help police Turkey's shores as 24 more migrants drowned en route to Greece and tens of thousands of others remained stranded at the Turkish-Syrian border. In the latest in a grim litany of migrant boat sinkings, 24 people, 11 of them children, drowned when their boat went down off the northwestern coast of Turkey, the Dogan news agency reported.

The migrants, whose nationalities were not known, were trying to reach the Greek island of Lesbos. Two people were rescued by the Turkish coastguard, which was were still scouring the sea for other victims.

The drownings came as German Chancellor Angela Merkel held talks with Turkish leaders on reducing the influx of migrants to Europe, and as 30,000 more Syrians fleeing the civil war massed along Turkey's border in the hope of receiving sanctuary.

Merkel said Turkey and Germany would ask NATO to help police the Turkish coast to prevent traffickers from packing migrants into overloaded boats for the perilous crossing to Greece.

The two countries would ask a meeting of NATO defence ministers starting Wednesday to discuss the situation in Syria "as well as whether, and to what extent, NATO can help in monitoring the situation at sea and lend support to Frontex and Turkish coastguards", she said after meeting Prime Minister Ahmet Davutoglu in Ankara. Turkey has been receiving mixed messages from Europe on how to handle the migrant tide.

Ankara, which has already taken in an estimated 2.7 million Syrian refugees, is under pressure to prevent migrants continuing across the Mediterranean to Europe while also being urged to open its doors to another batch of arrivals.

An estimated 30,000 Syrians who fled a Russian-backed regime offensive on opposition strongholds in northern Aleppo region have been camped out for days around the Bab al-Salama border gate, across from Turkey's Oncupinar crossing.

So far Turkey has only allowed medical emergencies through. "Obviously, as always, we will provide for our Syrian brothers and accept them when necessary," Davutoglu said. But he warned: "No one should assume that just because Turkey is taking in all the refugees that it should be expected to shoulder the refugee burden alone."

Ankara has long pushed for a safe zone inside Syria, where people could seek shelter while waiting for the war to end instead of piling across the border.

On Monday, Turkish aid groups began distributing tents to refugees on the Syrian side of the border and sent in truckloads of aid.

Merkel, whose country has received over one million migrants in the past year, said she was "horrified" by the suffering of the families stranded in the cold and wet around the border gate.

Many refugees are reportedly sleeping in fields and on roads in the area, whick lies only about 30 kilometres (20 miles) north of Aleppo.

The Turkish Humanitarian Relief Foundation, which is providing food for 20,000 refugees, said it had set up a camp with a capacity of 10,000 near Bab al-Salama, on top of eight camps for the internally displaced already run by Turkish agencies in the area.

"Our operations are aimed at taking care of people inside Syria," Serkan Nergis, a spokesman for the foundation, told AFP by phone.

Kerem Kinik, vice president of the Turkish Red Crescent, said there was "a de facto safe zone near the Turkish border". "Since February 5 we have sent roughly 2,000 tents and 6,000 blankets, as well as food," he added.

Mohammad Rahma, a 15-year-old who was blinded in a Russian air strike a month ago and wore bandages on his eyes, was among the few allowed cross into Turkey for medical treatment, accompanied by his father Ahmad. "We've been living out in the open because we don't have any place to stay," Ahmad told AFP.

Top diplomats from countries trying to resolve Syria's five-year conflict, which has claimed 260,000 lives and displaced half the population, are set to meet on February 11 after peace talks in Geneva collapsed last week.

The talks foundered as Syrian government forces closed in on Aleppo city in their biggest push since Russia intervened in September in support of President Bashar al-Assad, which has left mainstream rebels in disarray.

Regime troops have set their sights on Tal Rifaat - one of the last rebel strongholds in Aleppo province, which lies 20 kilometres from the Turkish border.

Late Sunday night, regime forces seized control of Bakfeen, a village just five kilometres south of Tal Rifaat. The roughly 350,000 civilians trapped inside rebel-held parts of Aleppo face the risk of a government siege, a tactic employed to devastating effect against other former rebel bastions.