It follows crisis talks in Damascus to allow humanitarian aid to reach besieged areas, which the Syrian government has approved for seven areas.
Tensions along the Turkey-Syria border are mounting.
Syrian government forces, backed by Russian air strikes, have made their way to within 25 kilometres of Turkey's frontier.
Kurdish YPG fighters have pushed forward, too.
Turkish leaders claim they are working together.
Turkish president Recep Tayyip Erdogan says the government-Russian operation is aimed at creating a corridor for Kurdish fighters aligned with the Democratic Union Party, or PYD.
"As you know, right now, Russia's brutal operation with the Syrian regime is underway. These brutal attacks targeting civilians aim to form a belt for the PYD and the ground element of those that is being handled by the YPG. Those who have helped these terrorist organisations will not be forgiven by history."
Some of Turkey's allies have criticised recent shelling against Kurdish fighters in Syria.
They fear it is increasing the risk of a military confrontation along the Turkey-Syria border.
President Erdogan has defended Turkey's actions, and Prime Minister Ahmet Davutoglu says Turkey is taking preventative measures to avoid further escalation.
"The objective of the precautions taken by our security forces against Russia, Bashar al-Assad and the PYD is to stop the games of those trying to drag Turkey into war by creating security risks on the border. I would like to stress once again, Turkey will continue to take precautionary measures to avoid the war."
Still, Turkey is prepared.
Turkish officials have said they would back a ground operation in Syria but only with its allies, including the United States, the United Arab Emirates and Saudi Arabia.
Iran foreign minister Mohammad Javad Zarif says the suggestion is concerning.
"We believe that's dangerous, an attempt to get others involved even in a larger number and more dangerous extent in the fighting in the region. I believe everybody should put their forces together to find a peaceful solution, not to create more danger and more hostility in the region. Everybody knows that that statement is simply a political ploy in order to get others in."
Lebanon's Hezbollah leader Sayyed Hassan Nasrallah says Turkish and Saudi ground troops in Syria would just be a guise for the allies to make gains in a proxy war.
"They want to come looking for a foothold while saying that they are fighting Daesh."
Meanwhile, the United Nations' Syria envoy, Staffan De Mistura, has held crisis talks in Damascus with Syrian foreign minister Walid al-Moualem.
The Syrian government has approved access to some besieged areas.
The deputy spokesman for the UN secretary-general, Farhan Haq, says UN convoys are expected to begin moving in days.
"The government of Syria has approved access to seven besieged areas. And those include Deir al-Zor, Foua and Kfarya in Idlib, and Madaya, Zabadani, Kfar Batna and Mouadamiya al-Sham in rural Damascus. Humanitarian agencies and partners are preparing convoys for these areas to depart as soon as possible."
It follows international condemnation of air strikes in Syria that hit four hospitals and a school earlier this week.
The act has been called a war crime.
Russia says it "categorically rejects" accusations against it over the bombing of hospitals in Syria.
Government spokesman Dmitry Peskov says those who make such statements are not capable of backing them up with proof.
A spokesman for the UN office of the High Commissioner for Human Rights, Rupert Colville, says investigations to determine whether the strikes were deliberate will take time.
"I can't really point the finger, but, clearly, Russian planes and Syrian planes are very active. And we would urge those who are dropping bombs and missiles out of the sky to take far more care, because the number of hits on civilians is just astronomical since this conflict began, and it's completely outrageous. All the norms and rules and standards of conduct of warfare have been just swept aside in Syria. Everything you can think of has been broken."
The World Health Organisation estimates 60 per cent of the public hospitals and nearly half of the primary health centres have been closed since the conflict began five years ago.
UNICEF spokesman Christophe Boulierac says the rate of attacks on schools is also alarming.
"Attacks on schools are also becoming commonplace in Syria. And last year alone, UNICEF was able to verify 42 attacks on schools. But, but, this is really a tip of the iceberg.* One in four schools in Syria cannot be used right now because they have been destroyed, damaged. We think that more than 50,000 teachers have fled the country and many hundreds have been killed."
