Turkey has reacted with anger after the French Senate approved a bill making it a crime to deny genocide was committed by Ottoman Turks against Armenians during World War I.
The Turkish foreign ministry branded the decision "irresponsible" and threatened swift retaliatory measures.
Armenia says that up to 1.5 million people died in 1915-16 as the Ottoman empire split.
Turkey rejects the term genocide and says the number was much smaller.
The bill will now be sent to President Nicolas Sarkozy to be signed into law, which he is expected to do before the end of February.
Correspondents say the move threatens to cause a serious rift between France and Turkey, who are Nato allies.
"France opened a black page in its history," said Volkan Bozkir, head of the Turkish parliament's foreign affairs committee, on Twitter.
Turkey's ambassador to France, Tahsin Burcuoglu, said the vote could cause a "total rupture" of relations between the two countries.
The foreign ministry statement hinted that the decision was influenced by looming presidential elections in France. An estimated 500,000 ethnic Armenians live in the country.
"We strongly condemn this decision which is... an example of irresponsibility," the statement said.
"Turkey is committed to taking all the necessary steps against this unjust disposition which reduces basic human values and public conscience to nothing."
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.
Turkish Prime Minister Recep Tayyip Erdogan is expected to outline possible retaliatory measures against Paris in parliament on Tuesday.
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).
Armenia, meanwhile, 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.
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".