LONDON (BLOOMBERG) - After years of needling his Nato partners, Turkish President Recep Tayyip Erdogan is finding that he needs them after all.

As Turkey slides towards war with Russian-backed Syrian forces, Ankara has appealed to the US and European allies for support in a conflict that risks undermining the friendly ties he has built with Moscow. The about-turn comes as the threat rises of a mass refugee movement towards Turkey, and of the defeat of Turkish-backed rebels in Syria.

Ankara's answer is to reach out to Washington to ask for a pair of Patriot missile-defence batteries to be deployed on the Syrian border. It needs the US-operated Patriots to deter Russian air strikes in support of an offensive on Idlib, the last rebel stronghold in Syria, by forces loyal to President Bashar al-Assad. Turkey also signalled its readiness to accept similar support from European allies.

The request is an abrupt change of tack for Erdogan after years of goading the US and European partners, and underlines how much is at stake for Turkey as it wades into the Syrian conflict on the opposing side to Russia. While Turkey insists it will avoid any confrontation with Russian forces, the pressure on Erdogan to respond is rising as the toll of Turkish casualties mounts.

"We're on the edge of the precipice and we need to come to a deal," said Irina Zvyagelskaya, a Middle East expert at the state-funded Institute of Oriental Studies in Moscow.

The latest Turkish deaths this week brought home the dangerous and unpredictable nature of the situation, and "should be a wake-up call," she said.

RUSSIAN MISSILES

Erdogan held a call on Friday with German Chancellor Angela Merkel and French President Emmanuel Macron, stressing the need for "strong support" to stop the aggression of the Syrian regime and its supporters in Idlib and to prevent a humanitarian crisis, his office said in a statement. That is after Merkel and Macron discussed Idlib with Russian President Vladimir Putin on Thursday.

Erdogan spoke by phone with Putin later on Friday, and urged him to "restrain" the Syrian regime in Idlib, the Turkish president's office said in a statement. "It is out of the question for us to withdraw from there unless they stop the oppression," Erdogan said earlier in the day.

Turkey has wrangled with the US over the Patriot system for years. The Trump administration refuses to sell Patriots to Turkey unless Ankara first scraps its purchase of an advanced Russian S-400 missile-defence system. Washington considers the S-400 a threat to Nato capabilities in general and specifically to its next generation F-35 fighter plane. The US sees a unique linkage between the S-400 and the Patriot issues.

When he took delivery of the S-400 missiles last year, Erdogan, who has developed good relations with Putin, had been convinced that the US couldn't just replace Turkey with another strategic ally. The calculus has now changed as Turkey has been stunned by the death of more than a dozen of its soldiers in air strikes and artillery fire in Idlib over the space of three weeks.

"The latest killing of two Turkish soldiers after a Russian air strike in Idlib on Thursday amounts to a serious split in ties with Moscow," said Nihat Ali Ozcan, a strategist at the Economic Policy Research Foundation in Ankara. "Further escalation of tensions with Russia may prompt Ankara to review its alliances."

ACTIVATING SYSTEM

For now, though, Turkey is unwilling to make the concessions that Washington is demanding. In order for delivery of the Patriots to take place and for Turkey's suspension from the F-35 programme to be revoked - a consequence of its S-400 purchase - the US wants Ankara to guarantee that it will never operate the Russian missiles. Erdogan's administration insists that guarantee won't be forthcoming.

"Without doubt, Turkey will activate the S-400s in spring," Turkey's Defence Minister Hulusi Akar told CNN-Turk television on Thursday.

While saying that his country has "no intention to face off with Russia" over Idlib, Akar added that Russia should not intervene in Turkey's push back of Syrian forces to their positions. That move is in line with an agreement reached between Erdogan and Putin in the Black Sea resort of Sochi to de-escalate the situation in Syria's northwestern province, he said. In their call on Friday, Erdogan told Putin that resolution of the crisis unfolding in Idlib hinges on full implementation of the Sochi deal, according to the presidency statement.

Russia appears determined to back a full capture of the Idlib deescalation zone regardless, even if it remains unclear how fast it will push for the endgame. Such a move could allow Assad to expand links between the capital, Damascus, and the former business hub of Aleppo, and even to declare final victory in the near decade-long civil war.

A potential compromise could lie in allowing Assad to take control of the main highways in return for halting the offensive, according to Zvyagelskaya of the Institute of Oriental Studies. That could at least offer a temporary resolution, she said.

REFUGEE THREAT

Turkey, meanwhile, is hindered by considerations of the impact of a mass exodus north towards its borders of one to two million refugees from Idlib. While Turkey plans to shelter those fleeing within Syria, the situation would still add to the burden of hosting 3.6 million Syrian refugees already. It has won expressions of support from the US, but with Russia dominating Syrian air space, it's unclear how much assistance Washington or Nato would be able or willing to provide.

The tensions are testing defence, trade and even tourism relations between Turkey and Russia, which attaches importance to its relationship with Ankara, "not just for Syria but more broadly for Russia's confrontation with the West and Nato," said Joost Hiltermann, programme director for the Middle East and North Africa at the International Crisis Group.

Turkey is part of the Western alliance and doesn't want to lose that status, Hiltermann said in an interview in Moscow. But it's also been using Russia "to push back against policies that it doesn't like from its Western partners," notably US support for Kurdish militants viewed as a threat by Ankara, he said.

Both sides face "a very difficult negotiation," said Hiltermann. "But it is really about Russia deciding what it wants from its relationship with Turkey."