The U.N. Security Council will hold an emergency meeting on Friday at Russia's request to discuss the crisis in Syria, diplomats said.

The meeting scheduled for 2000 GMT was called to address Turkey's proposal for ground forces to be deployed in Syria, the Russian foreign ministry said in Moscow.

President Recep Tayyip Erdogan said on Friday that Turkey had "no doubt" that Syrian Kurdish fighters were behind an attack on a convoy of military buses in Ankara that left 28 people dead.

Russia is accusing Turkey of helping jihadists recruit fighters from the Caucasus and Central Asia to fight in Syria, according to a letter sent to the U.N. Security Council.

Russian Ambassador Vitaly Churkin said in the letter dated February 10 that recruiters from the Islamic State group had reportedly established a network in the Turkish city of Antalya for foreign fighters from the former Soviet Union.

European Union leaders meeting in Brussels on Thursday piled pressure on Turkey to curb the flow of migrants to Europe in line with an aid-for-cooperation deal signed last year.

Pressure to enforce the deal is growing as EU officials say thousands of migrants are still crossing the Aegean daily from Turkey after more than one million made the perilous journey last year in the greatest such movement since World War II.

Turkey said Tuesday it wanted a ground operation in neighboring Syria with its international allies, as a U.N. envoy held talks in Damascus aimed at saving a troubled ceasefire plan.

Tensions escalated over Russia's air war in support of Syrian President Bashar al-Assad, with Ankara branding it "vile, cruel and barbaric" and EU President Donald Tusk saying it "leaves little hope" of a solution.

The United States on Monday urged Turkey and Russia to avoid any further escalation after the two traded verbal blows over their respective military actions in war-torn Syria.

"It is important that the Russians and Turks speak directly, and take measures to prevent escalation," a State Department spokesperson told AFP.

Turkey will not allow the Syrian town of Azaz just across from the Turkish border to fall under the control of Syrian Kurdish fighters, Prime Minister Ahmet Davutoglu said on Monday.

"We will not let Azaz fall," Davutoglu was quoted as saying by the private NTV television on his plane en route to an official visit to Ukraine.

The Turkish army struck positions of Kurdish fighters inside Syria for a second day Sunday in response to incoming fire, state media said, as an explosive standoff between Ankara and Syrian Kurds intensified.

The army hit Democratic Union Party (PYD) targets around the Syrian town of Azaz using howitzers stationed on the Turkish side of the border, the state-run Anatolia news agency reported.

Turkey and Saudi Arabia could launch a ground operation against Islamic State jihadists in Syria, the Turkish foreign minister said Saturday, adding the kingdom was already sending jets to a Turkish base to attack the extremists.

The coordinated plans by Riyadh and Ankara, who are pursuing an increasingly tight alliance, add a new element to the explosive situation in Syria where Russia has been backing a successful regime offensive against rebels.

Some 100,000 Syrian refugees are being looked after in camps inside Syria close to the Turkish border, including 35,000 who this month fled a Russian-backed regime offensive in northern Aleppo province, a top Turkish official said Friday.

Turkish Deputy Prime Minister Yalcin Akdogan, whose country has come under increasing pressure to open its border to people fleeing the violence, said the refugees were being accommodated in nine camps just across the border with Syria.