ANKARA - Turkey called on Russia and Iran on Wednesday to pressure Syrian authorities to halt a military offensive in Syria's rebel-held northwestern province of Idlib launched by Damascus despite an international deal to reduce hostilities there.Nearly 3 million people are believed to be in the Idlib region, their numbers swelled by fighters and civilians who fled Syrian army advances elsewhere in Syria. Fresh conflict could trigger more displacement on Turkey's southern border.Turkish Foreign Minister Mevlut Cavusoglu said Russia and Iran must fulfill their duties under a joint accord reached with Turkey last year under which the three countries announced a "de-escalation zone" in Idlib.He said advances by the Syrian army and allied forces into Idlib could not have taken place without the support of Moscow and Tehran, which have both backed President Bashar al-Assad in Syria's six-year-old conflict."Iran and Russia need to carry out their responsibilities. If you are guarantors, which you are, stop the regime," Cavusoglu told the state-run Anadolu news agency in an interview broadcast on Turkish television channels.Cavusoglu's ministry summoned the Iranian and Russian ambassadors on Tuesday to complain about violations of the Idlib de-escalation zone, and he said President Tayyip Erdogan might call Russia's Vladimir Putin on the issue.Turkey, which has been fiercely opposed to Assad, has recently been working with his allies Russia and Iran for a political resolution to the conflict. But Cavusoglu said the Idlib offensive was endangering those efforts. "This isn't a simple air strike, the regime is advancing into Idlib. The goal is different here," he said. "If the aim here is to make some unwilling opposition groups go to Sochi, it will backfire," he added, referring to Russia's plans to host a meeting on Syria at the end of this month.The Syrian army, supported by Iran-backed militias and Russian air power, began an offensive in late October in Hama province. By the end of last week, they had advanced into Idlib, close to an insurgent-held military airport.60,000 DISPLACEDThe fighting and air strikes have forced more than 60,000 people to leave their homes since Nov. 1, according to the U.N. Office for the Coordination of Humanitarian Affairs (OCHA).The main rebel force in the northwestern province of Idlib is Tahrir al-Sham (HTS), spearheaded by the former al Qaeda affiliate in Syria that was known as Nusra Front."What I am seeing here is the use of the presence of al Nusra and HTS as an excuse to attack civilians and moderate oppositions," Cavusoglu added.Under last year's agreement with Iran and Russia, Turkey says it has deployed troops to observation points in northern Idlib, about 60 km (40 miles) north of the latest Syrian army offensive.Cavusoglu said Ankara would host a meeting on Syria with like-minded countries after the summit in Russia's Sochi. With Russian and Iranian backing, government forces have recovered large swathes of territory from rebels and Islamic State militants over the past year.Assad and his allies command the single largest chunk of Syria, followed by US-backed Kurdish militias who control much of the north and east Syria and are more concerned with shoring up their regional autonomy than fighting Damascus.