* Turkey has 12 observation posts in northwest Syria
* Erdogan says 30-35 Syrians "neutralised" in retaliation
* Turkey told Russia to stand aside, Erdogan says 

President Tayyip Erdogan said on Monday Turkey will continue to retaliate after Syrian government shelling killed four of its troops and wounded nine in Syria's northwest Idlib region, where Turkish forces have bulked up in recent days.
Erdogan said initial indications show 30-35 Syrians were "neutralised" in Turkey's response to what the government called intense shelling of its soldiers. He said Turkey has told Russian counterparts "they need to stand aside" in the escalating conflict.
Syrian President Bashar al-Assad's forces, backed by Russian air power, have recently made advances in Idlib, prompting Turkey to warn it may launch a military operation there unless the fighting is halted.
"We have responded in kind to these attacks and will continue to do so, whether it is with our artillery or mortars," Erdogan told reporters in Istanbul.
"We are determined to continue our operations for the security of our country, people and our brothers in Idlib," he said. "Those who question our determination will soon understand they made a mistake."
A Turkish security official told Reuters that the shelling which killed the soldiers occurred in the area of Saraqeb town, 15km to the east of Idlib city.
"Following the developments in Idlib in recent weeks, serious support was provided over the weekend to the troops, equipment and vehicles in the region," the official said.
The Idlib region is the last major rebel-held stronghold in Syria's nearly nine-year-old war and Erdogan accuses Russia of violating agreements to reduce the fighting in the region, a charge which Moscow denied on Friday.
Turkey, which already hosts 3.6 million refugees from Syria, fears a fresh wave of migrants from Idlib. It has 12 military observation posts around the region, set up under a 2017 agreement with Russia and Iran. Several of them have since been surrounded by advancing Syrian government forces.
A spokesman for Erdogan's AK Party said Turkey will view Syrian government forces around the observation posts in the region as "targets".
The Syrian Observatory, a UK-based war monitor, said some 320 Turkish trucks and military vehicles entered Idlib at Kafr Lusin crossing on Sunday, much more than usual, and went south.
Turkey's defence ministry said Syrian shelling was carried out against its reinforcements, which were meant to prevent clashes in Idlib, despite prior coordination of their positions.
Erdogan said if talks between diplomats and generals fail to get results he will contact Russian President Vladimir Putin directly to try to resolve the situation.
"We told especially Russian counterparts that they are not our counterparts here, that it is the (Syrian) regime directly, and that they need to stand aside," Erdogan said. "This is not okay, we are giving martyrs here, but our armed forces and our artillery... are keeping them under fire."
He added F-16s are involved in Turkey's operation against 40 points in Idlib.
Russia's TASS news service said no air strikes were carried out in the fighting.
The US special envoy for Syria said on Thursday the Idlib fighting raised the spectre of an international crisis. 
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