Turkey has urged all parties in northern Syria for calm and warned against provocations amid allegations by the Bashar Assad regime and its allies of chemical weapon usage in Aleppo, which were followed by Russian airstrikes in Idlib.

"Despite the Idlib agreement that we reached with Russia [that] received international support, we know there are some who have been trying to undermine it. There are reciprocal accusations. [Our] defense ministers and head of intelligent services discussed this with Russian [counterparts]. I will also discuss it with my counterparts as soon as possible. We should not be provoked," Foreign Minister Mevlüt Çavuşoğlu said yesterday in a press meeting in Istanbul.

On Sunday, warplanes struck opposition territory in northwestern Syria for the first time since Turkey and Russia agreed to create a buffer zone in the province of Idlib in September, the Syrian Observatory for Human Rights said. The U.K.-based monitoring group said the Assad regime ally Russia "likely" carried out the airstrikes that hit suburbs west of Aleppo city, near Idlib.

The Syrian opposition alliance denied Sunday any involvement in a chemical weapons attack on regime-held Aleppo and accused the Assad regime of staging the attack to undermine the cease-fire.

"We at the National Liberation Front deny the criminal, lying regime's allegations that revolutionaries targeted the city of Aleppo with any missiles and especially not any containing chlorine gas," a written statement published by the opposition alliance read after Syrian media accused opposition groups of using toxic gas.

In relation to the issue, opposition commander Abdel-Salam Abdel-Razak said yesterday the opposition does not possess poisonous gases or the capabilities to launch them.

Opposition spokesman Mustafa Sejari dismissed the claims that they came after regime shells landed in opposition-held areas, violating the Sochi deal that was reached by Russia and Turkey to set up a demilitarized zone. Sejari also added that the regime is trying to undermine the cease-fire.

On Saturday, the Observatory said shelling by the regime killed nine civilians, including seven children, in the planned demilitarization zone in Idlib.

Defense Minister Hulusi Akar and his Russian counterpart Sergei Shoigu discussed on Sunday the recent developments in Idlib. Also, Russian military spokesman Maj. Gen. Igor Konashenkov told reporters on Sunday in Moscow that Russian warplanes destroyed militant positions in northern Syria blaming them for the poison gas attack on Aleppo.