French senators vote later on Monday on a bill to make it illegal to deny that the mass killing of Armenians by Ottoman Turks nearly a century ago was genocide, raising the prospect of a major diplomatic rift between two NATO allies.

Lawmakers in the lower-house National Assembly voted overwhelmingly in December for the draft law outlawing genocide denial, prompting Ankara to cancel all economic, political and military meetings with Paris and recall its ambassador for consultations.

The bill, which has been made more general so that it outlaws the denial of any genocide, partly in the hope of appeasing the Turks, will be debated from 3 p.m. (1400 GMT) in the upper house before a final vote.

Armenia, backed by many historians and parliaments, says about 1.5 million Christian Armenians were killed in what is now eastern Turkey during World War One in a deliberate policy of genocide ordered by the Ottoman government.

The Ottoman empire was dissolved soon after the end of World War One, but successive Turkish governments and the vast majority of Turks feel the charge of genocide is a direct insult to their nation. Ankara argues there was heavy loss of life on both sides during fighting in the area.

Turkish Foreign Minister Ahmet Davutoglu said Ankara would take new measures against France unless the bill was rejected.

If every (EU) parliament implements decisions reflecting its own historical views a new Inquisition period will begin in Europe, Davutoglu was reported as saying by Dogan news agency. We all know what happened during the Inquisition in the Middle Ages. Unfortunately the revival of this is shameful for France.

Thousands of Turks from across Europe demonstrated in central Paris at the weekend and about 200 Franco-Turks protested on Monday in front of the senate. They waved their French voting cards and banners with slogans including: It's not up to politicians to invent history.

The Socialist Party, which has had a majority in the Senate since elections in the upper house late last year, and the Senate leader of President Nicolas Sarkozy's UMP party, which put forward the bill, have said they will back the legislation.

But a non-binding Senate recommendation last week said the law would be unconstitutional, and after weeks of aggressive Turkish lobbying there are suggestions the outcome will be closer than anticipated.

If adopted, Sarkozy should then ratify the bill with the process to be completed before parliament is suspended in February ahead of presidential elections.

The bill can still be rejected by the country's highest court if that body considers the text unconstitutional.

Turkey calls the bill a bid by Sarkozy to win the votes of 500,000 ethnic Armenians in France in the two-round presidential vote on April 22 and May 6.

Sarkozy wrote to Turkish Prime Minister Tayyip Erdogan last week saying the bill did not single out any country and that Paris was aware of the suffering endured by the Turkish people during the final years of the Ottoman empire.

French Foreign Ministry spokesman Bernard Valero on Monday called on Turkey not to overreact, adding that Paris considered Ankara a very important ally.

Engin Solakoglu, first secretary at the Turkish embassy in Paris, said: France can't continue to say that Turkey is an important ally when it votes laws against it.

European Union candidate Turkey could not impose economic sanctions on France, given its World Trade Organisation membership and customs union accord with Europe.

But the row could cost France state-to-state contracts and would create diplomatic tension as Turkey takes an increasingly influential role in the Middle East.

The bill mandates a maximum 45,000-euro fine and a year in jail for offenders. France passed a law recognising the killing of Armenians as genocide in 2001.

(Additional reporting by Emile Picy and Lucien Libert in Paris and Daren Butler in Istanbul)