France's Constitutional Council ruled Tuesday that a French law concerning the mass killings of Armenians a century ago violates the country's constitution.

French President Nicolas Sarkozy, who had personally backed the law, immediately said he would ask the government to prepare a new bill taking into account the council's ruling.

The law passed by France's parliament in December makes it a crime to deny that the killings of some 1.5 million Armenians by Ottoman Turks in 1915 constituted genocide. The council ruled the law would violate freedom of expression and speech, which are guaranteed by the French constitution.

Turkey, which says there was no systematic campaign against Armenians, has strongly opposed the French law.

The head of a French Armenian organization, meanwhile, sharply criticized the ruling, saying it was the result of Turkish lobbying.

Relations between France and Turkey have suffered since the law's passage, with Turkey suspending its military and economic cooperation with France after the lower house approval of the measure in December. The French Senate gave the law the green light in late January.

"We have been totally outraged by the Constitutional Council's decision at its very core, which is based on politics rather than on legal grounds," said Franck Mourad Papazian, president of the Council of Coordination of Armenian Organizations in France.

The measure had also sowed divisions in France, with some lawmakers expressing some of the same concerns as Ankara, notably that not allowing people to deny that the mass killings of Armenians nearly a century ago was genocide impinges on freedom of expression.

Turkey's foreign minister welcomed the decision, saying it was "pleasing that a grave mistake has been corrected by France's highest legal body."

In a written statement, Ahmet Davutoglu said he hopes France adopts "a constructive approach in regard to the handling of the conflict between Turkey and Armenia in a just and scientific manner and contributes to its solution rather than deepening it."

"Such an approach would contribute to improvement of Turkish-French relations in every field," Davutoglu said.

France's relations with Turkey were already strained, in large part because Sarkozy opposes Turkey's entry into the European Union.

Sarkozy's office said in a statement he recognized the "immense disappointment and profound sadness" of the law's supporters. Sarkozy said he will meet soon with representatives of France's Armenian community, many of whom had welcomed the law's passage with a swell of relief.

France formally recognized the 1915 killings as genocide in 2001, but provided no penalty for anyone refuting that. The law struck down Tuesday had set a punishment of up to one year in prison and a fine of euro45,000 ($59,000) for those who deny or "outrageously minimize" the killings, putting such action on par with denial of the Holocaust.

Most historians contend the killings of the Armenians constituted the first genocide of the 20th century. But the issue is dicey for any government that wants a strong alliance with Turkey, a rising power. In Washington, President Barack Obama has stopped short of calling the killings genocide.

An estimated 500,000 Armenians live in France, and many have pressed to raise the legal statute regarding the massacres to the same level as the Holocaust by punishing the denial of genocide.

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Associated Press writer Selcan Hacaoglu in Ankara and APTN producer Oleg Cetinic in Paris contributed to this report.