The Turkish prime minister has said a bill passed by the French parliament on the mass killing of Armenians under Ottoman rule is "racist".
Recep Tayyip Erdogan told the Turkish parliament in Ankara that the bill "murdered freedom of thought".
French President Nicolas Sarkozy is expected to sign the bill into law before the end of February.
Armenia says that up to 1.5 million people died in 1915-16 as the Ottoman empire split.
Turkey, which rejects the term "genocide", has said the number of deaths was much smaller.
Defenders of the bill point out that it covers all acts of genocide.
'Footsteps of fascism'
"This is a racist and discriminatory approach and if you cannot see this, then you are deaf to the footsteps of fascism in Europe," Mr Erdogan said on Tuesday, a day after the bill was adopted by the French Senate.
Turkey, he added, hoped for the success of a French appeal against the bill to the constitutional commission.
"We will wait and see the developments and decide on our reply to them," he said.
Earlier, the Turkish foreign ministry warned that Turkey planned to respond with unspecified measures against France.
It appeared to tie the bill to France's forthcoming elections.
"It is further unfortunate that the historical... relations between the Republic of Turkey and France have been sacrificed to considerations of political agenda,'' the ministry said.
An estimated 500,000 ethnic Armenians live in the country.
Correspondents say the French bill threatens to cause a serious rift between France and Turkey, who are Nato allies.
The Turkish government argues that judging what happened in eastern Turkey in 1915-16 should be left to historians, and that the new French law will restrict freedom of speech.
France has already recognised the killings as a genocide but the new bill means anyone denying it faces a year in jail and a fine of 45,000 euros ($57,000).
The killings are regarded as the seminal event of modern Armenian history, a tragic bond uniting one of the world's most dispersed peoples.
Among the other states which formally recognise them as genocide are Argentina, Belgium, Canada, France, Italy, Russia and Uruguay, but the UK, US, Israel and others use different terminology.
Armenia has described Monday's vote - by 127 votes to 86 - as "historic".
"This day will be written in gold not only in the history of friendship between the Armenian and French peoples, but also in the annals of the history of the protection of human rights," said Minister of Foreign Affairs Edward Nalbandian.
However, in neighbouring Azerbaijan, a senior member of the ruling party said France's credibility as a mediator with Armenia over the Nagorno-Karabakh dispute had been damaged and it should abandon its role there.
"France has betrayed its mediator mission," said Ali Ahmadov, executive secretary of the New Azerbaijan Party.
Ankara froze ties with France after the lower house passed the bill last month.
The proposed law had been made more general - outlawing the denial of any genocide - but still failed to appease Ankara.
Last week, President Sarkozy wrote to Mr Erdogan saying the bill did not single out any country.
He said France recognised the "suffering endured by the Turkish people" in the final years of the Ottoman empire.
French foreign ministry spokesman Bernard Valero called on Turkey not to overreact, saying Paris considered Ankara a "very important ally".