The current rivalry between France and Turkey may not be new, but it appears to have reached new heights – or rather lows.

"All you can say about a head of state who treats millions of members of various religious communities like this is you should first go get your mental health checked," Turkish President Recep Tayyip Erdogan said last week in a televised speech, referring to French President Emmanuel Macron. "Macron needs mental treatment," he added.

Erdogan's words were an apparent response to Macron's doubling-down on a national campaign to fight Islamic extremism in France and his defense of free speech, including the right to satirize elements of Islam.  

French presidential officials deemed Erdogan's words "unacceptable" and "outrageous" and recalled the country's ambassador from Ankara to Paris for consultations.

Turkey, in turn, called for a boycott of French products. Other Muslim countries have followed suit, and protests against France have also taken place, prompting Paris to warn citizens there to "exercise extreme caution."

The intensified Franco-Turkish spat comes as France has been roiled by a streak of terror attacks by suspected Islamic extremists. Two weeks ago, Samuel Paty, a 47-year-old history teacher, was beheaded by a Russian-born Muslim teen. Paty had recently shown his class a cartoon of the Prophet Muhammad taken from the French satirical magazine Charlie Hebdo. Several members of the magazine's staff were killed by Islamic extremist terrorists after the image's initial publication in 2015.

Most recently, three people were killed Thursday in Nice in what is suspected to have been another terror attack related to Islamic extremism.

A 'volcanic atmosphere'

Turkey's Foreign Ministry condemned Thursday's attack and sent condolences to France, even as it remains embroiled in the diplomatic feud whose vitriolic rhetoric has surprised experts.

"I am really surprised as to how verbally aggressive Erdogan has become in this dispute," Didier Billion, deputy director at the French Institute for International and Strategic Affairs, a Paris-based think tank, told DW.

"The atmosphere is now outright volcanic – even though the rivalry in itself is not new, as France and Turkey have for a while been on opposite sides in issues such as the wars in Syria and Libya, energy exploration in the Mediterranean Sea and the conflict in Nagorno-Karabakh," he explained.

"Although the spat won't lead to outright war, it will make cooperation between France and Turkey in areas such as the fight against terrorism and economic projects a lot more difficult," Billion added.

France and Turkey playing to domestic audiences

Billion believes both leaders are caught up in a battle of egos and trying to push their profiles at home.

"Erdogan is fanning the flames of nationalism, and Macron wants to address the French's fear of Islamism and crime to appeal to right-wing voters ahead of the presidential elections in 2022," he said.

Jean Marcou, head of the department of international relations at the University of Sciences Po Grenoble, also sees Turkish media playing a role in Erdogan's ability to shape the disagreement.

"Erdogan is benefiting from the fact that Turkish-language media have hardly covered the teacher's beheading, i.e. the reason behind Macron's new measures to fight Islamist extremism," he told DW. "Taking the new measures out of context makes it easier for Erdogan to depict Macron as someone who lost his mind."

Meanwhile, in France, Charlie Hebdo's latest front-page cartoon, showing Erdogan in his underpants drinking a can of beer and revealing a Muslim woman's naked backside, has provided Erdogan with a new reason to be incensed. He has called the satirists "scoundrels" and threatened to take legal and diplomatic actions.

Read more: France Muhammad cartoon row: What you need to know

'An emerging battle line in the Middle East'

In addition to domestic positioning, experts also see both Erdogan and Macron making international calculations.

"Macron is … trying to strengthen his international profile for a world after Brexit and where NATO plays a less important role with US President Trump increasingly questioning the alliance's role," Marcou said.

Asli Aydintasbas, senior policy fellow at the European Council on Foreign Relations, a pan-European think tank, sees the presidents as vying for regional influence. 

"This seems like a golden opportunity for Erdogan to come forth as the defender of Islam and the Sunni leader of the Arab world and for Macron to further increase his sphere of influence in the Middle East," she told DW, adding this was tantamount to an "emerging battle line in the Middle East."

EU sanctions against Turkey 'unavoidable'

Nevertheless, Aydintasbas thinks Turkey could be shooting itself in the foot.

"During the last meeting of the European Council, the camp around Germany, Italy, Spain, et cetera, won the argument, and sanctions were discarded in favor of a positive agenda with regards to Turkey," she explained. "Now, these countries will have to rally around France, which has a tougher stance and is pushing for sanctions."

Countries such as Germany, Italy and the Netherlands have in fact expressed solidarity with France and Macron over the past few days.

Sinan Ulgen, chairman of the Center for Economics and Foreign Policy Studies, an Istanbul-based think tank, and a visiting scholar to the Carnegie Europe think tank in Brussels, reckons sanctions are now unavoidable, even though they are likely to be limited in their extent.

"The EU needs unanimity for any measures imposed, and as Turkey is an important partner, the sanctions will probably be rather light and toothless," he told DW.

Even should that be the case, Ulgen still believes the Franco-Turkish spat will have a long-term impact.

"It will widen the civilizational divide between Turkey and the West, which is based on Islamophobia," he said. "Tensions between those supporting freedom of expression and those wanting to protect religious values are rising further."