Update: Here are the latest headlines out of Russia where the defense ministry is at wit's end with the Turks.

RUSSIAN DEFENCE MINISTRY SAYS 'TERRORISTS' IN SYRIA'S IDLIB AND ALEPPO PROVINCES CONTINUE TO RECEIVE WEAPONS AND REINFORCEMENTS FROM TURKISH TERRITORY - INTERFAX

TURKEY IS LAUNCHING 'MASSED' ARTILLERY STRIKES ON SYRIAN GOVT FORCES AND 'SYRIA'S PATRIOTIC OPPOSITION' - RIA CITES RUSSIAN DEFENCE MINISTRY

Turkey shelled Syria for a fourth consecutive day on Tuesday as Ankara steps up efforts to bolster rebels in the face of an advance by the Kurdish YPG. “As many as 150 terrorists were killed during the 4-day-long shelling targeting PYD points,” the pro-government Yeni Safak wrote today, adding that “the PYD, backed by both the US and Russia, is working with President Bashar al-Assad to control areas along the Turkish border.”

The move by Russia and Iran to encircle Aleppo and cut rebel supply lines to Turkey has allowed the YPG to advance on towns near the border, effectively consolidating the group’s grip on northern Syria, where they’ve been highly successful at holding large swaths of territory.That’s an especially undesirable outcome for Ankara where President Recep Tayyip Erdogan is hell bent on rolling back a groundswell of popular support for the pro-Kurdish HDP which, at least in AKP’s mind, is merely the political arm of the PKK.

Erdogan doesn’t distinguish between the PKK (which both Turkey and the US officially designate as a terror group) and the YPG. The US, on the other hand, openly supports the Syrian Kurds and has backed their advances with airstrikes. Ankara fears that if the YPG are allowed to bridge the territory they control east of the Euphrates with territory they control west of the river, they will effectively establish a proto-state on the border which would embolden the PKK to try something similar in southeast Turkey where some Kurds are already pushing for autonomy.

Throw in the fact that the towns the YPG are seeking to capture are held by rebels Ankara supports in the faltering bid to oust Bashar al-Assad, and there’s every reason to suspect that Turkey will not only persist in the shelling of Azaz, but will in fact invade Syria. You know, “to fight ISIS.”

On Tuesday we got still more indications that a major escalation in Syria is imminent when Turkey said it would “definitely” participate in a ground operation. “It’s impossible to end the war without it,” an official told Bloomberg, speaking on the condition of anonymity. You see how that works? It’s the same logic that France employed when officials declared that the best way to halt the refugee crisis is to bomb Syria. It’s “impossible” to the end the war in Syria without ... going to war in Syria.

The official also said there was no plan for a “unilateral” ground operation by Turkey or Saudi Arabia, but according to Yeni Safak newspaper’s Ankara correspondent, Turkey is planning to send troops 10km into Syria to establish “a safe zone.” Ankara is apparently concerned that if Azaz-Tal Rifaat area falls to the YPG, 400K-500K refugees might mass at the Turkish border.

Now bear in mind, it’s not entirely clear why that would be the case. There are indeed questions about the YPG’s human rights record, but they’re hardly ISIS or al-Nusra. Why civilians would flee by the hundreds of thousands is far from evident and it certainly seems as though Turkey is just looking for an excuse to ensure that its supply lines to al-Nusra and other Sunni rebels aren’t cut, and to keep the Kurds from controlling key border towns. The “safe zone” plan - which is reminiscent of the absurd “ISIS-free” zone idea from last August - would reportedly require US support. America, Yeni Safak says “has never been sincere about Assad going from the very beginning.”

Additionally, Turkey now says 500 FSA troops have traveled to Azaz via Turkey to beat back the YPG advance. Here’s Yeni Safak again:

As many as 500 fighters from the Free Syrian Army (FSA) have entered Syrian territory through Turkey to defend Azaz town, besieged by Syrian Kurdish militia forces. Russian-backed Syrian pro-government forces have cut off the last supply route, known as the Azaz corridor, linking partially opposition-held Aleppo with Turkey. If the last corridor completely falls, the rebel groups could lose the quarters of Aleppo they currrently control, mostly in the east. It means that Assad's regime, backed by Iran and Russia, and the PYD will gain the power to control the entire Turkish-Syrian border. PYD-linked armed groups' attempt to advance to Aleppo and open harrassment fire into Turkish territory has prompted the Turkish military to retaliate with F?rt?na howitzers. Syrian opposition forces have marched to the area which Turkish military targeted in lines with the rules of engagement. One of them is Sham Legion, known as Homs Legion, fighting in northern Idlib against forces, loyal to Assad. Sham Legion has sent its fighters to the besieged town to stop the advance of PYD's armed groups. They appear to be protecting the corridor leading to the opposition-held eastern Aleppo. The reports said that Sham Legion, an umbrella group of 19 different organizations some of which were previously affiliated with Syrian Muslim Brotherhood, had dispatched 500 fighters to conflict in the key town through Turkey's Cilvegöz border crossing three days ago. The fighters crossed into Syria under Turkey's supervision after the government had approved their crossing into Syrian territory through the country's border.

It's easy to see why the Turks are getting worried. On Monday, the YPG seized control of Tal Rifaat, a town between Aleppo and Azaz. "Their latest advances are part of a bid to unite the Kurdish town of Afrin in western Aleppo province with Kurdish areas to the east," Al Arabiya notes. "We will not let Azaz fall," Turkish PM Ahmet Davutoglu said. "The YPG will not be able to cross to the west of the Euphrates (River) and east of Afrin."

Obviously, simply shelling Azaz and Tal Rifaat isn't going to do the trick. If Turkey wants to halt the advance, they're going to have to send troops or F-16s, and the latter option is a virtual impossibility given Russia's deployment of S-400s in the country.

Meanwhile, Moscow and Ankara continue to accuse one another of being terrorists. What should be clear from the above is that there's no telling who the Islamist rebels fighting to keep the Azaz corridor open are. It's the same mishmash of Sunni militants fighting everywhere else in western Syria and it seems likely that al-Nusra elements are present as well. As Russian PM Dmitri Medvedev recently told TIME, "they're all bandits."

Yes, rampant banditry, facilitated by the Turks.

Of course Russia isn't innocent in all of this either. Although it's impossible to verify the veracity of the reports, it seems possible that several Russian strikes hit hospitals on Monday, killing scores of civilians, some women and children. Ankara of course seized on the opportunity to accuse the Russians of being terrorists. "These attacks that we strongly condemn are unconscionable and obvious war crime under international law," a statement from the Turkish foreign ministry reads. "If Russian Federation does not end those attacks immediately - which remove peace and stability - it is inevitable that Russia will face bigger and more serious results."

The takeaway from all of this is simple: escalation imminent.