Turkey on Wednesday called on Russia and Iran, the two chief allies of President Bashar al-Assad's regime in Syria, to halt an air offensive on the rebel-held Idlib province near the Turkish border.

Ankara has been working closely with Russia and Iran to end the Syrian conflict over the last months but has stepped up pressure on Moscow and Tehran as the bombardments on Idlib intensified.

"Iran and Russia should fulfil their responsibility. If you are guarantors -- and you are -- they should stop the regime," Foreign Minister Mevlut Cavusoglu told the official Anadolu news agency.

"This is not a simple air offensive. The regime is advancing inside Idlib. They have a different intention."

Cavusoglu emphasised that in efforts to bring peace to Syria, Russia and Iran were the "guarantors" of the regime side and Turkey of the opposition.

Idlib province is almost entirely controlled by anti-government forces that are dominated by a jihadist outfit known as Hayat Tahrir al-Sham (HTS) consisting mostly of former fighters from the Al-Nusra Front, an Al Qaeda affiliate.

Ankara has already summoned the Russian and Iranian ambassadors, in the biggest public flare-up of tensions with Moscow and Tehran in months.

It conveyed "uneasiness" to the Russian ambassador Tuesday, calling the strikes a "violation of the borders of the Idlib de-escalation zone" established by Turkey, Iran and Russia, according sources at the foreign ministry.

Cavusoglu said 95 percent of the violations in Idlib were carried out by the regime and the groups backing the regime.

President Recep Tayyip Erdogan could speak by phone with Russian leader Vladimir Putin to discuss the situation, he added.

"We cannot remain indifferent. We have exerted so many efforts and we cannot waste them."

The escalation comes as Russia is hoping to hold a Syria peace congress in its Black Sea resort of Sochi on January 29-30 bringing together all the main parties in the conflict.

A previous attempt in November to convene talks in Sochi failed due to disagreements between the prospective participants.

But in a major potential obstacle for Sochi, Turkey says it will oppose any talks involving the Syrian Kurdish militia the Peoples' Protection Units (YPG), which Ankara views as a terror group.

Cavusoglu repeated Turkey's red line over its presence in Sochi by saying that: "We have said we will not be in any environment... where the YPG is present."

Source: AFP