* Western partners pledge up to 950 mln euros each
* Gazprom to shoulder 50 pct cost of the pipeline
* Uncertainty remains over final approval (Adds details on financing, Gazprom CEO quotes)
By Alissa de Carbonnel and Maya Nikolaeva
PARIS, April 24 (Reuters) - Western partners of gas giant Gazprom agreed on Monday to provide half the financing for the 9.5-billion euro ($10.32 billion) Nord Stream 2 pipeline, removing a big hurdle for a Russian plan to pump more gas to Europe.
The commercial endorsement of the project by Western firms offers Russian state-owned Gazprom, which already supplies around a third of the EU's gas, fodder to counter critics of a project that has divided opinion in Europe.
Eastern European and Baltic countries say a new pipeline carrying Russian gas across the Baltic will make the EU a hostage to Moscow, while those in northern Europe -- especially main beneficiary Germany -- see the economic benefits.
At a signing ceremony in Paris, Uniper, Wintershall, Shell, OMV and Engie agreed to each loan 10 percent of the cost of the venture, or up to 950 million euros each.
Gazprom will remain the sole shareholder, shouldering 50 percent of the cost of the 55 billion cubic metre pipeline, which is due to start operating in 2019.
"It's a breakthrough," Gazprom Chief Executive Alexei Miller told Reuters. "It's a firm confirmation of foreign participation in the project, it's an important financial basis for the project to be completed by the end of 2019."
Opponents of the project also worry it would sharply reduce the need for Russia to export gas through Ukraine, depriving Kiev of lucrative transit fees.
Last July, Gazprom's Western partners withdrew from pledges to provide 1.2 billion euros of equity for the pipeline, a twin to Nord Stream 1, which began pumping in 2011, after Poland's cartel office blocked its clearance.
The European firms have been in talks since on how to share the financial burden, and despite Monday's agreement industry sources said financing details were still being worked out.
German energy group Uniper said in a statement it was looking into a potential partnering to share its tab for the 1,225 km (760 mile) pipeline, which will pump gas to Europe via the Baltic Sea to Germany.
Austrian oil and gas group OMV said it would provide long-term financing to secure 30 percent of its share of project costs of the pipeline from Russia, and turn to project financing for the rest.
French gas and power group Engie's Chairman Gerard Mestrallet told reporters the new financial structure would allow Western partners to resolve Polish objections.
"I hope that the pan-European support will bring financial aid to the great project led by our Gazprom friends," Mestrallet said at the signing ceremony.
The timing of the announcement is likely to influence deliberations by EU nations, including France and Germany, on whether to give the European Union a mandate to negotiate with Russia over objections to the pipeline.
"The sceptics and the pessimists have been proven wrong," former German Chancellor Gerhard Schroeder, now chairman of the board of directors of Nord Stream 2, said. "Nord Stream 2 is on track. Pipe production is moving forward at full speed."
However, uncertainty remains over the project's final approval as the European Commission is politically opposed to the project and has argued that it falls foul of EU gas market liberalization rules.
EU sources say the Commission has sought to cultivate uncertainty in a bid to scare off Western investors that would stall construction until after 2019, thereby depriving Gazprom of a lever in negotiations on a new gas transit contract with Ukraine due to expire that same year.
But the EU's own lawyers as well as the German energy regulator, the Bundesnetzagentur, have rejected the Commission's bid for EU energy rules to be applied to an import pipeline that is outside the bloc's legal border. ($1 = 0.9207 euros) (Additional reporting by Dimitry Zhdannikov in London, Vera Eckert in Frankfurt and Kirsti Knolle in Vienna; Editing by Vladimir Soldatkin and Susan Thomas)