Top diplomats from Iran and six world powers geared up on Tuesday for a crucial round of talks aimed at forging a lasting and potentially historic agreement over Tehran's nuclear program.

A senior U.S. official said negotiators from the five permanent members of the U.N. Security Council plus Germany were already in Vienna, preparing for the official start on Wednesday.

The number of French Jews emigrating to Israel rose nearly four-fold in the first quarter of the year and could touch a record in 2014, a Jewish organization said Monday.

The Jewish Agency for Israel, a global body responsible for the immigration and absorption of Jews into Israel, said 1,407 people left France for Israel between January and March against 353 people a year earlier.

The foreign ministry said Monday that France and Germany intend to prevent Syrians living in their countries from voting in Syria's presidential election, expected to return President Bashar Assad to power.

Germany and France are "preventing Syrians living in their territory from voting", the foreign ministry said.

French President Francois Hollande said in Azerbaijan Monday that cooperation between Europe and ex-Soviet countries should not be seen as infringing on anyone else's interests, a clear reference to Moscow amid the crisis in Ukraine.

"The European Union's Eastern Partnership is not directed against anyone, but should encourage greater trade and investment", the French leader said after meeting with Azerbaijani counterpart Ilham Aliyev.

French President Francois Hollande called Sunday for African leaders to hold a summit in Paris on security in west Africa focusing on the the Islamist sect Boko Haram who have abducted scores of schoolgirls in Nigeria.

"I suggested, with Nigerian President Goodluck Jonathan, a meeting of Nigeria's neighboring countries," he said during a visit to the Azerbaijan capital Baku. The meeting will take place Saturday "if the countries agree," he added.

French Foreign Minister Laurent Fabius has ruled out going to war with Russia over Ukraine, but warned more sanctions will be leveled against Moscow if it tries to undermine the May 25 presidential vote.

"We cannot accept the annexation or the fact that Ukraine would be controlled or invaded," Fabius, who visits the United States this week, said in an interview published Sunday in The Washington Post.

French President Francois Hollande on Sunday denounced separatist votes by pro-Russian rebels in eastern Ukraine as "null and void."

On a visit to the ex-Soviet republic of Azerbaijan, Hollande said the votes taking place in Donetsk and Lugansk made "no sense" and that only Ukraine's presidential vote on May 25 mattered.

French President Francois Hollande starts a three-day visit to the South Caucasus on Sunday as he seeks to bolster European ties on Russia's southern doorstep amid the crisis in Ukraine.

Hollande was due to arrive in the Azerbaijani capital Baku around 6:00 pm (1300 GMT) Sunday, on the same day separatists in eastern Ukraine held referendums on breaking away from the country.

EU heavyweights France and Germany warned on Saturday that it could be weeks after May 25 elections before a new head to the European Commission is chosen by bloc leaders.

"There is a meeting of European leaders and heads of government set for May 27, but the decision will not be made on the Tuesday or Wednesday following the elections," said German Chancellor Angela Merkel during a visit by French President Francois Hollande to northern Germany.

French President Francois Hollande said Saturday the sale of two Mistral warships to Russia would continue "for now" despite the West's worsening relations with Moscow over the Ukraine crisis.

"The contract was signed in 2011, it is being carried out and will be completed by next October," said Hollande during a press briefing in Germany, where he met with Chancellor Angela Merkel.