NATO chief Jens Stoltenberg says Russia's airstrikes in Syria are undermining efforts to find a non-military solution to the conflict.
Stoltenberg made the comment Friday as he arrived in Amsterdam for a meeting of European Union defense ministers.
He said the "intense" Russian airstrikes are mainly targeting opposition groups and are causing increased tensions, as well as violations of NATO airspace and Turkish airspace.
In another development, Syrian government forces supported by Russian warplanes recaptured a rebel-held town near Deraa, according to Hezbollah's Al Manar television and a Syrian monitoring group Friday.
That news came a day after a U.N.-led donor conference pledged $10 billion for Syria humanitarian relief.
Syrian forces seized Ataman, about 3 kilometers north of Deraa in the country's south. The assault was aided by dozens of airstrikes believed to have been carried out by Russian planes, the Britain-based Syrian Observatory for Human Rights said.
In recent days, the Syrian army and its allies have also made significant advances against rebels in the northern province of Aleppo.
The Russian-backed assaults were in part responsible for derailing peace talks in Geneva earlier this week, with Syrian government officials walking away from the talks after claiming that they had ended the rebel siege of two Shi'ite villages in Aleppo, handing President Bashar al-Assad's government a major victory.
Meanwhile, Turkey's Prime Minister Ahmet Davutoglu said Friday up to 70,000 people were headed toward his country to escape a Russian-backed offensive led by government troops around Aleppo.
The U.N. Security Council is scheduled to meet Friday for consultations with U.N. envoy Staffan de Mistura over the breakdown in negotiations, which were suspended until February 25.