Nato allies France and Turkey exchanged angry accusations over Nagorno-Karabakh on Wednesday, where Azerbaijan and Armenian fighters were engaged in a fourth day of fighting in the worst flare-up of violence in decades.
Both sides reported shelling along the line of contact separating the ethnic Armenian enclave from Azerbaijan, as fighting that has killed dozens threatened to escalate into full-blown war.
Azerbaijan vowed to continue fighting until all Armenian troops withdrew from the disputed territory.
"Azerbaijan is resolutely determined to continue the counter-offensive operation until its sovereignty and territorial integrity is fully restored," the country's foreign ministry said in a statement.
War in the energy-rich Caucasus could shake oil markets, increase tensions within Nato, and draw in regional powers Turkey and Russia.
Moscow maintains good relations with both of the former Soviet republics but has a security treaty with Armenia, while Turkey supports Azerbaijan.
France’s President Emmanuel Macron said Turkey's incendiary rhetoric was encouraging Azerbaijan to reconquer the breakaway region.
France “remains extremely concerned about the warlike messages from Turkey in the past few hours, which amount to giving Azerbaijan the go-ahead for what would be a reconquest of Nagorno-Karabakh,” Mr Macron told a news conference in Latvia.
However he said he had no proof of direct Turkish involvement in the fighting.
“At this stage, we have no evidence that would allow us to talk about a regionalisation of the conflict,” he added.
But Turkey’s statements favouring Azerbaijan were “inconsiderate and dangerous,” he said.
In response, Turkey’s foreign minister Mevlut Cavusoglu said France’s position amounted to supporting Armenia’s “occupation” of part of Azerbaijan’s territory.
Mr Cavusoglu said Turkey would "do what is necessary" if Azerbaijan requested military support, echoing earlier remarks by Turkish President Recep Tayyip Erdogan.
Armenia has repeatedly accused Turkey of involvement in the fighting, and on Wednesday shared images showing the wreckage of what it said was an SU-25 warplane shot down by a Turkish jet on Tuesday. Ankara and Azerbaijan denied that a Turkish F-16 had downed an Armenian plane.
Turkish-backed Syrian mercenaries are also reportedly fighting for Azerbaijan in the conflict, with BBC Arabic reporting that one fighter said at least 10 of his comrades had been killed and dozens wounded.
Hundreds of fighters from the Turkish-backed opposition Syrian National Army had travelled to Azerbaijan via Turkey, BBC Arabic reported, drawn by monthly salaries of $2,000.
Nearly 100 people have died in the fighting so far, most of whom are ethnic Armenian separatists, officials say, but also 17 civilians on both sides, including women and children.
Azerbaijan's defence ministry said Armenian shelling injured civilians in Tartar on Wednesday morning, while Armenia said bombing from an Azerbaijani plane killed three civilians in the city of Martakert.
The current clashes in the breakaway territory are some of the worst since the 1990s, when Azerbaijan lost control of the enclave in fighting that killed 30,000 people and displaced hundreds of thousands.
In 1994, ethnic Armenians declared independence, which has not been recognised internationally.
Both sides are resisting international calls for a ceasefire.
Mr Macron said he would discuss the conflict in telephone calls with Russian President Vladimir Putin on Wednesday evening and with Donald Trump on Thursday.
France, Russia and the United States co-chair the Minsk Group of 13 countries which aims to resolve the conflict.
Armenian Prime Minister Nikol Pashinyan said Wednesday that peace talks with Azerbaijan under Russian mediation would be inappropriate.
"It isn't very appropriate to speak of a summit between Armenia, Azerbaijan and Russia at a time of intensive hostilities," Mr Pashinyan told Russia's Interfax news agency.