At least 33 refugees are believed to have drowned off Turkey's coast as they tried to make their way to a Greek island, underscoring the migrant crisis facing Europe’s leaders on the day German Chancellor Angela Merkel agreed on a set of measures with her Turkish counterpart to help ease the plight of Syrian refugees.

Turkish state-run media reported that 22 refugees died in one maritime accident and that a rescue operation was underway for the remaining passengers. Separately, the private news agency Dogan said 11 migrants died and three were rescued when another boat sank further south, off the coast of Dikili in the province of Izmir.

Such drownings are becoming all-too routine as hundreds of thousands of people flee warzones and poverty in parts of the Middle East and Africa.

More than 900,000 people fleeing Syria, Afghanistan and other war-torn or impoverished countries arrived in Greece from Turkey last year, often risking their lives in the short but perilous sea crossing in overloaded boats. Hundreds have died making the attempt.

Germany, which has let in more than a million asylum seekers last year, forged an agreement Monday with Turkey on a set of measures to deal with the Syrian refugee crisis, including a joint diplomatic initiative aiming to halt attacks against Aleppo, Syria's largest city from which many citizens have fled.

On Monday in Ankara, officials from the two countries added that they would push to curb illegal migration.

German Chancellor Angela Merkel, who was in the Turkish capital for talks on how to reduce the influx of refugees into Europe, said after discussions with Turkish Prime Minister Ahmet Davutoglu that she is “not just appalled but horrified” by the suffering caused by Russian bombing in Syria.

Merkel said that Turkey and Germany will push at the United Nations for everyone to keep to a UN resolution passed in December that calls on all sides to halt without delay attacks on the civilian population.

She said: “We have been, in the past few days, not just appalled but horrified by what has been caused in the way of human suffering for tens of thousands of people by bombing, primarily from the Russian side.”

“Under such circumstances, it's hard for peace talks to take place, and so this situation must be brought to an end quickly,” Merkel said.

The EU has promised $3.3 billion of aid in return for Ankara's help in stopping the flow of new arrivals on its shores, most of whom make their way through Turkey.

The bloc's leaders have said Ankara is obliged to keep its frontiers open to refugees, while also pressing for tighter border controls for those entering Europe.

Turkey's Oncupinar border crossing, which faces the Bab al-Salama frontier post inside Syria, remained closed on Sunday as refugees, mostly women and children, gathered there for a third day waiting for the gate to open.

The governor of Kilis province, Suleyman Tapsiz, said that Turkey was taking care of the 30,000-plus refugees who had gathered around the nearby Syrian city of Azaz over the space of 48 hours.

Another 70,000 may head for the frontier if Russian air strikes and Syrian regime military advances continued in Aleppo, he added.

Turkey has vowed to help the crowds of people, including many women and children, but has not opened its borders, and aid agencies have warned they are facing a “desperate” situation as they wait for help.

Turkish President Recep Tayyip Erdogan said Turkey was ready "if necessary" to let in Syrian refugees trapped on its border.

“The regime has now blocked a part of Aleppo … Turkey is under threat,” Erdogan told reporters on his plane returning from Senegal on Saturday.

“If they reached our door and have no other choice, if necessary we have to and will let our brothers in,” he added.

Fadi Hajjar, a Syrian activist with the Aleppo Media Center based in Gaziantep, Turkey, told Al Jazeera that there were between 30,000 and 50,000 people waiting at the border.

“This number is likely to increase in the coming days,” he said on Sunday. “Some villages in Aleppo have been completely emptied of people.”

Al Jazeera and wire services